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DENTAL  AND  OEAL  RADIOGEAPHY 


DENTAL  AND  ORAL 

RADIOGRAPHY 


A  TEXTBOOK  FOR  STUDENTS  AND  PRACTITIONERS 
OF  DENTISTRY 


BY 


JAMES  DAVID  McCOY,  M.S.,  D.D.S.,  F.A.C.D. 

PROFESSOR   OF   ORTHODONTIA   AND    RADIOGRAPHY,    COLLEGE    OF   DENTISTRY, 
UNIVERSITY  OF   SOUTHERN   CALIFORNIA,   LOS   ANGELES,   CALIFORNIA 


WITH  116  ILLUSTRATIONS 


THIKD  EDITION 


ST.  LOUIS 

C.  V.  MOSBY  COMPANY 

1922 


Copyright,  1916,  1918,  1922,  by  The  C.  V.  Mosby  Company 
(All  rights  reserved) 


Printed  in  U.  S.  A. 


Press  of 

The  C.    V.   Mosby   Coijnpany 

St.  Louis,  Mo. 


■  t.  '    y    '•.,#1*1...    \  • 


A/ 
^0 


\\llcci 


PREFACE  TO  THIRD  EDITION 


During  the  past  few  years,  much  of  value  has  been  added  to 
dental  radiography.  This  has  not  come  entirely  from  new  in- 
ventions or  new  developments  in  technic,  but  has  been  the 
result  of  its  more  universal  adoption  in  dental  practice  with  a 
consequent  closer  analysis  of  its  true  values  and  possibilities. 

With  the  development  of  any  new  science  there  is  always 
born  an  enthusiasm  which  is  apt  to  get  out  of  boimds  and  carry 
its  victims  beyond  the  range  of  good  balance,  but  with  the  back- 
ward swing  of  the  pendulum  which  comes  with  more  complete 
knowledge,  affairs  assume  more  rational  proportions.  This  is 
true  of  the  present  status  of  dental  and  oral  radiography. 
Without  depreciating  its  value,  for  in  many  instances  it  is  abso- 
lutely indispensable,  we  must  realize  that  it  is  but  one  important 
link  in  the  chain  of  successful  diagnosis.  To  regard  it  other- 
wise is  both  unjust  to  it  and  to  our  profession. 

In  the  revision  of  the  text  and  illustrations,  the  writer  has 
endeavored  to  condense  the  material  as  much  as  would  be  just 
and  consistent  with  the  subject  and  has  kept  uppermost  in  mind 
the  needs  of  the  dental  student.  The  dental  practitioner  of  ex- 
perience has  many  avenues  for  increasing  his  knowledge  of  this 
field  and  it  is  hoped  that  the  contents  of  this  volume  may  inspire 
the  dental  student  to  do  likewise  when  more  ample  opportunities 
are  offered. 

The  author  gratefully  acknowledges  the  assistance  given  him 
by  Dr.  Leo  M.  Baughman,  Dr.  A.  R.  Ebenreiter  and  Dr.  Carroll 
W.  Jones  who  aided  him  in  the  selection  of  many  of  the  radio- 
grams used  as  illustrations  in  Chapter  X,  and  for  their  valuable 
counsel. 

James  D.  McCoy. 

Los  Angeles,  California. 


663185 


PREFACE  TO  SECOND  EDITION 

During  the  preparation  of  the  second  edition  of  this  book  the 
author  has  endeavored  at  all  times  to  keep  in  mind  the  needs  of 
the  beginner  in  radiography  rather  than  consider  matters  of  in- 
terest to  those  who  have  progressed  beyond  this  stage. 

That  radiography  is  essential  in  the  practice  of  dentistry  is 
no  longer  a  debatable  question.  The  wide  interest  being  mani- 
fested in  it  by  our  profession  and  the  numerous  instances  where 
dentists  are  installing  their  own  x-ray  laboratories  bear  elo- 
quent testimony  of  this  fact.  While  the  author  is  willing  to  plead 
"guilty  to  a  great  degree  of  enthusiasm"  regarding  the  value 
of  the  x-ray  in  dentistry,  he  feels  that  he  is  within  reasonable 
bounds  in  asserting  that  the  x-ray  has  done  more  to  improve 
dentistry  than  any  other  agent  that  has  come  into  it  during  the 
past  ten  years.  If  it  were  of  value  ''in  root  canal  operations 
only"  the  benefits  to  this  field  alone  would  justify  the  foregoing 
statement,  for  we  must  all  acknowledge  that  as  commonly  prac- 
ticed in  the  past  this  branch  represented  the  greatest  short- 
coming of  our  profession. 

Fortunately  root  canal  work  does  not  represent  the  only  field 
in  dentistry  where  the  radiogram  is  a  benefit,  for  it  has  been 
demonstrated  that  it  is  of  equal  value  and  in  fact  is  often  abso- 
lutely essential  in  the  other  branches  of  practice.  These  facts 
are  not  only  now  fairly  well  appreciated  by  dentists,  but  the 
laity  have  been  quick  to  grasp  them  with  the  result  that  den- 
tists who  attempt  certain  operations  without  radiographic  guid- 
ance are  open  to  censure  from  their  patients. 

The  awakening  of  the  rank  and  file  of  the  profession  to  the 
necessity  of  a  more  universal  adoption  of  the  x-ray  has  been 
slow,  and  it  is  doubtful  if  some  will  ever  become  fully  conscious, 
as  they  continue  to  exhibit  a  lethargy  toward  this  field  which 
is  either  indicative  of  lack  of  foresight  or  sheer  laziness. 

In  contrast  to  such,  it  is  refreshing  to  recall  that  some  mem- 
bers of  our  profession  were  quick  to  see  the  possibilities  to  den- 

6 


PREFACE  '  i 

tistry  offered  through,  the  adoption  of  the  x-ray.  Conspicuous 
among  these  was  Dr.  C.  Edmond  Kells,  of  New  Orleans,  who  in 
1896  (within  the  year  following  the  discovery  of  the  x-ray) 
installed  x-ray  equipment  in  his  office  and  applied  it  to  his 
dental  practice.  So  great  were  his  convictions  and  so  genuine 
was  his  enthusiasm  that  in  July,  1906,  he  took  his  x-ray  equip- 
ment to  Ashville,  N.  C,  and  there  gave  a  clinic  before  the  South- 
ern Dental  Association.  Dr.  Kells  was  the  first  dentist  to  make 
radiograms  by  placing  small  films  in  the  mouth,  and  he  also 
originated  the  plan  of  placing  diagnostic  wires  in  the  roots  of 
teeth. 

Among  those  who  shared  Dr.  Kells'  foresight  during  those 
pioneer  days  and  adopted  the  x-ray  as  part  of  dental  practice 
are  numbered  such  men  as  Drs.  Van  Wort,  M.  L.  Rhein,  E.  W. 
Caldwell,  T.  P.  Hinman,  and  Weston  A.  Price. 

Within  the  last  few  years  a  large  number  of  our  dental  schools 
have  included  radiography  in  their  teaching  curriculums  and 
some  have  even  shown  the  foresight  of  establishing  it  as  a  dis- 
tinct department  with  equal  rank  and  consideration  with  the 
other  important  branches.  This  will  in  time  bear  fruit  which 
will  result  in  a  more  adequate  appreciation  of  the  merits  and 
possibilities  of  the  x-ray  and  its  inseparable  relationship  to 
dentistry. 

The  author  wishes  to  gratefully  acknowledge  the  assistance 
given  him  in  the  preparation  of  this  edition  by  Dr.  Julio  Endel- 
man,  whose  friendly  criticism  and  interest  have  been  a  constant 
source  of  help.  Grateful  acknowledgment  is  also  made  to  Dr. 
Richmond  C.  Lane,  who  was  kind  enough  to  contribute  several 
radiograms  from  practical  cases  illustrating  root  canal  opera- 
tions, root  resections,  and  cysts.  The  author  has  also  been  aided 
by  various  manufacturers  of  x-ray  equipment  who  have  fur- 
nished many  cuts  of  value  to  the  text,  and  last,  but  not  least, 
the  publishers  have  by  their  cooperation  and  patience  through 
many  delays  rendered  less  irksome  the  task  of  the  writer. 

James  D.  McCoy. 

Los  Angeles,  Cal. 


PKEFACE  TO  FIRST  EDITION 

This  book  has  been  written  primarily  as  a  textbook  for  stu- 
dents of  dentistry.  It  is  essentially  a  book  for  beginners,  and 
as  the  majority  of  the  dental  profession  are  at  present  to  be 
regarded  as  beginners  in  this  comparatively  new  branch  of  den- 
tistry, the  author  entertains  the  hope  that  it  will  prove  of  inter- 
est to  practicing  dentists  Avho  appreciate  the  value  of  the  x-ray, 
and  are  desirous  of  adding  radiography  to  their  accomplish- 
ments. 

A  few  years  ago  the  x-ray  was  considered  in  the  light  of  a 
cultural  asset  to  dentistry,  but  today  the  far-seeing  members 
of  our  profession  have  awakened  to  the  fact  that  it  is  a  real 
necessity. 

The  x-ray  will  give  the  maximum  amount  of  service  in  dental 
practice  only  to  such  of  our  profession  who  master  the  technic 
of  radiography,  and  in  addition  are  possessed  of  an  accurate 
knowledge  of  the  anatomy  and  pathology  of  the  dental  and  oral 
structures. 

The  author  is  indebted  to  the  pioneers  in  dental  radiography 
who  have  so  generously  contributed  to  its  literature.  Of  these, 
much  of  value  has  been  derived  from  the  writings  of  such  men  as 
Drs.  A,  H.  Keteham,  Weston  Price,  Sidney  Lange,  Howard  R. 
Raper,  F.  L.  R.  Satterlee  and  Edward  H,  Skinner. 

During  the  preparation  of  this  work,  the  author  has  been 
aided  by  various  manufacturers  of  x-ray  equipment  who  have 
generously  furnished  cuts  whenever  requested.  Grateful  ac- 
knowledgment is  also  made  to  Dr.  J.  R.  McCoy  and  to  Laura 
Spruill  who  have  made  the  drawings  used  as  illustrations,  and 
last  and  by  no  means  least,  to  the  publishers  who  have,  through 
their  forbearance  and  many  courtesies,  lessened  the  burdens  of 
the  writer. 

James  D.  McCoy. 

Los  Angeles,  Cal. 


CONTENTS 

PAGE 

CHAPTER  I 
Introdtjction 17 

CHAPTER  II 

The  Nature  OF  THE  X-BAY  AND  Its  Discovery 23 

CHAPTER  III 
High  Tension  Electric  Currentsi — Magnetism — Electromagnetic 

Induction        .      .  32 

CHAPTER  IV 
Rhumkorff  or  Induction  Coil — Tesla  or  High  Frequency  Coil — 

Intebrupterless  Transformer 44 

CHAPTER  V 
Requisites  of  the  Dental  X-ray  Laboratory 61 

CHAPTER  VI 
Teciinic    of    Dental    and    Oral    Radiography — The    Intra-oral 

Method 77 

CHAPTER  VII 
Teciinic    of   Dental    and    Oral    Radiography — The    Extra-oral 

Method 93 

CHAPTER  VIII 
Technic  of  Dental  and  Oral  Radiography  (Continued) — Proper 

Tube  and  Current  Conditions 110 

CHAPTER  IX 
Correct  Exposure  and  Development  of  X-ray  Plates  and  Films    123 

CHAPTER  X 
The  Interpretation  of  Dental  and  Oral  Radiograms     ....     133 

CHAPTER  XI 
Indications   for   the   Use   of   the   X-ray   in   the   Practice   of 

Dentistry 154 

CHAPTER  XII 
Dangers  of  the  X-ray  and  Methods  of  Protection 186 

9 


ILLUSTRATIONS 

FIG.  PAGE. 

1.  William    Conrad   Eoentgen 24 

2.  Michael  Faraday 25 

3.  Sir  William  Crookes 26 

4.  Hcinrich  Hertz 27 

5.  The  action  of  iron  filings  in  forming  definite  curved  lines  about 

an  ordinary  bar  magnet 35 

6.  Diagrammatic  illustration  of  the  magnetic  lines  of  force     .      .  36 

7.  Diagrammatic  illustration  of  the  magnetic  field  surrounding  a 

coil  of  wire  through  which  an  electric  current  is  passing     .  37 

8.  An  iron  bar  placed  within  the  windings  of  a  solenoid  is  subject 

to  its  magnetic  field  and  becomes  a  magnet 38 

9.  Magnet  with  diagrammatic  illustration  of  "magnetic  lines  of 

force"    surrounding    it 39 

10.  Battery  from  which  an  electric  current  is  passing  through  the 

solenoid 40 

11.  Diagrammatic  illustration  of  the  essential  parts  of  an  induction 

coil 44 

12.  Diagram  of  the  electrolytic  interrupter 46 

13.  Diagram  of  the  induction  coil 47 

14.  Induction  coil  adapted  for  use  in  the  dental  x-ray  laboratory  50 

15.  Diagram  of  the  high  frequency  coil 53 

16.  The   working   principles   of   the   interrupterless  transformer     .  55 

17.  Interrupterless  transformer  adapted  for  use  in  the  dental  x-ray 

laboratory 56 

18.  Interrupterless  transformer  adapted  for  use  in  the  dental  x-ray 

laboratory 57 

19.  Step-up    transformer    unit 58 

20.  Step-up    transformer    unit 58 

21.  Step-up    transformer    unit 59 

22.  Diagram  of  an  x-ray  tube 64 

23.  Coil    or    transformer    tube 65 

24.  The  high  frequency  tube 66 

25.  Connecting  the  tube  to  the  x-ray  machine 67 

26.  The   hydrogen   tube 67 

27.  The  Coolidge  tube 69 

28.  The  tube  stand 70 

29.  Illustrating  reasons  for  using  the  tube  shield,  compression  dia- 

phragm, and  compression  cylinder 71 

30.  Leaded    glass    tube    shield 73 

11 


12  ILLUSTRATIONS 


PACK. 


31.  A  convenient  manner  of  arranging  the  necessary  apparatus  when 

not  in  use .  74 

32.  The  portable  dark  room 75 

33.  The  patient  holding  the  film  in  position  against  the  upper  teeth  81 

34.  Correct   and   incorrect   technic 82 

35.  Technic  for  the  upper  molar  teeth 84 

36.  Special  compression  cylinder  made  of  leaded  glass     ....  85 

37.  The  patient  can  hold  the  film  in  position  against  the  lower  teeth 

by  exerting  slight  jiressure  -with  the  finger 86 

38.  The   Leach   film   holder 88 

39.  The  Dorr  film  holder  with  detachable  handle 89 

40.  Diagram  of  complete  exposure  of  the  dental  arch     ....  89 

41.  Method  of  obtaining  radiograms  using  the  bite  method     ...  90 

42.  The  head-rest  of  the  dental  chair  with  its  many  adjustments  can 

easily  be  arranged  so  that  the  patient 's  head  may  rest  easily 

and  firmly  upon  it 93 

43.  Tube  stand  with  plate-rest  and  head-support 94 

44.  Tlie  arrangement  of  the  apparatus  preparatory  to  seating  the 

patient 96 

45.  The  patient  seated  and  the  apparatus  arranged  for  making  a 

radiogram  of  the  left  side 97 

46.  Plate  and  head-rest  support  for  extra-oral  radiograms     ...  98 

47.  Plate  and  head-rest  support  adjusted  to  the  arms  of  the  dental 

chair 98 

48.  Technic   for   the   left    side 100 

49.  Technic  for  the  right  side .  101 

50.  The   result   of   correct   technic 102 

51.  Incorrect  technic 103 

52.  The  result  of  incorrect  technic 104 

53.  Technic  for  radiographing  areas  in  the  upper  and  lower  jaws 

extending  from  the  median  line  to  the  first  premolar     .      .  105 

54.  The  structures  at  the  median  line  including  the  incisors,  both 

above  and  below  may  be  secured  in  this  way 106 

55.  Supporting  the  patient's  head  with  a  bandage  of  gauze  to  pre- 

vent movement 107 

50.     The  tube  connected  with  the  x-ray  machine 112 

57.  Diagrams  of  the  x-ray  tube 115 

58.  The  radiator  type  Coolidge  tube 116 

59.  Radiator  Coolidge  tube,  right  angle  type 116 

60.  X-ray-proof  film  and  plate  chest 124 

61.  Intra-oral  radiograms  of  groups  of  teeth  and  adjacent  tissues, 

under  normal  conditions 140 


ILLUSTRATIONS  13 

FIG.  PAGE. 

62.  Instances    where    inflammatory    processes    have    resulted    in    a 

hypertrophy  of  the  peridental  membrane  and   resultant  en- 
croachment upon  the  alveolar  structures 142 

63.  ■  Chronic  dento-alveolar  abscesses  with  cystic  formation      .      .      .     143 

64.  Three  instances  of  true  cysts  occurring  in  the  mandible      .      .      144 

65.  Eadioluceut    areas   adjacent   to    the   roots    of   teeth   which   are 

characteristic  of  necrosis  or  rarefying  osteitis     ....      145 

66.  Eadiopaque  areas  about  the  roots  of  teeth  or  in  the  alveolar 

bone  indicating  defensive  bone  reaction 146 

67.  Characteristic  appearance  of  the  investing  tissues  in  well  de- 

veloped pyorrhea  alveolaris 147 

68.  A  cuspid  tooth  lying  against  the  anterior  wall  of  tlie  antrum      .      149 

69.  A  radiogram  to  determine  the  state  of  dentition  of  the  right 

side  in  the  mouth  of  a  child  eleven  years  old 150 

'70.     Root  canal  fillings 151 

71-B.     Instances  where  the  roots  of  teeth  lie  in  elosie  proximity  to 

the  anti-um  or  accessory  antral  cells 152 

72.  Extra-oral  radiogram  of  the  right  side  made  for  purposes  of 

general  examination 156 

73.  Intra-oral  radiogram  used  as  a  means  of  confirmation  of   the 

findings  of  the   extra-oral  radiogram 157 

74.  Alveolar  abscesses  at  the  apex  of  each  bicuspid  root     .      .      .  157 

75.  Upper  bicuspid  teeth  with  abscesses 157 

76.  Severe   inflammatory   process   in   progress   about   upper   lateral 

incisor 157 

77.  Extra-oral  radiogram  of  the  lower  molars  showing  the  presence 

of  a  large  alveolar  abscess 158 

78.  Radiograms  showing  imperfectly  filled  canals,  diagnostic  wires 

in  place,  and  same  teeth  after  being  filled 159 

79.  Radiograms  showing  imperfectly  filled  canals,  diagnostic  wires 

in  place,  and  same  teeth  aftdr  being  filled 160 

80.  Radiogi'ams  showing  imperfectly  filled  canals,  diagnostic  wires 

in  place,  and  same  teeth  after  being  filled 160 

81.  Radiogram  showing  condition  present,  diagnostic  wires  inserted, 

root  canals  filled,  and  resection  of  roots 161 

82.  Radiograms  showing  central  incisor  before  resection,  after  re- 

section,  and  several  months   later,   showing  regeneration   of 
osseous  tissue 162 

83.  Upper  central  root  before  resection,  and  after  resection,  show- 

ing partial  regeneration 163 

84.  A  well-developed  case  of  pyorrhea  alveolaris  involving  the  molars 

and    incisors 164 

85.  An  unerupted  cuspid  tooth  making  an  attemi)t  to  erupt  under 

a    bridge 166 


14  ILLUSTRATIONS 

FIG.  PAGE. 

86.  Radiogram  made  to  be  sure  no  root  fragments  were  present  in 

the  tissues  under  the  bridge 166 

87.  Inflammatory  process  under  a  small  bridge 166 

88.  Extra-oral  radiograms  of  impacted  and  unerupted  third  molars  168 

89.  lutra-oral  radiograms  of  impacted  lower  third  molars  .  .  .  169 
90-A.  Large  cyst  in  the  mandible  lying  below  a  molar  tooth  .  .  170 
90-B.     Same  case  as  shown  in  97-A,  six  months  after  curettement, 

showing  partial  regeneration  of  the  osseous  structure     .      .      170 

91.  Large  abscess  with  cyst  formation,  involving  the  upper  central, 

lateral  and  cuspid  roots 171 

92.  Radiogram  revealing  the  fact  that  there  is  a  congenital  absence 

of  permanent  molars  on  the  left  side 172 

93.  Radiogram  revealing  the  fact  that  all  but  one  of  the  permanent 

molars  are  congenitally  absent  on  the  right  side     .      .      .      .      172 

94.  Unerupted  lower  second  bicuspid  for  which  space  must  be  made 

to  permit  its  eruption 174 

95.  Unerupted  cuspid  for  which   space   must   be  made  if   it  is  to 

erupt  in  its  normal  position 174 

96.  Unerupted  lower  lateral  incisor  for  which  space  must  be  made     175 

97.  Unerupted  lower  second  molar  prevented  from  erupting  through 

impaction  against  the  lower  first  molar 175 

98.  Unerupted  upper  bicuspid  teeth  Avhich  are   being  deflected  to 

the  lingual 176 

99.  Unerupted  bicuspid  teeth  which  are  rotated  and  erupting  to  the 

lingual 176 

100.  Radiograms   showing   unerupted   cuspid,    same    tooth   after   re- 

moval of  lateral  incisor  and  deciduous  cuspid,  showing  at- 
tachment for  moving  the  unerupted  tooth;  cuspid  tooth 
moved  down  to  the  point  of  eruption 177 

101.  Supernumerary  teeth.     Case  after  extraction 177 

102.  An  unerupted  lower  second  bicuspid  in  a  patient  twelve  years 

old 179 

103.  Unerupted  upper  and  lower  bicuspids  in  a  patient  eleven  years 

of  age 179 

104.  Unerupted  cuspid  teeth  whose  relationship  to  tlie  roots  of  the 

incisors  must  be  taken  into  consideration  during  tooth  move- 
ment     180 

105.  An  unerupted  lower  third  molar  which  is  crowding  the  incisors     181 

106.  An  erupting  lower  third  molar  which  has  been  responsible  for 

the  crowding  of  the  lower  incisors  and  cuspids     ....      181 

107.  Non-vital  tooth  being  used  as  an   anchor  tooth  and   non-vital 

tooth  which  was  considered  unsafe  for  anchorage     .      .      .      183 

108.  Supernumerary  upper  second  bicuspid 183 

1 09.  Lower  deciduous  central  incisors  having  the  appearance  of  super- 

numerary teeth 183 


ILLUSTRATIONS  15 

FIG.  PAGE 

110.  Radiogram   showing  either  an   anomalous   central  incisor   or  a 

central  incisor   lying  in   a   horizontal   position  to   the   other 

teeth 183 

111.  Patient  seated  and  the  apparatus  arranged  to  make  a  radiogi-am 

to  the  left  side 184 

112.  Patient  seated  and  the  apparatus  arranged  to  make  a  radio- 

gram of  the  right   side 184 

113.  An  x-ray  tube  inclosed  within  a  leaded  glass  tube  shield     .      .  191 

114.  Lead-lined  protection  screen 192 

115.  Lead-impregnated  glove 193 

116.  X-ray  protection  apron 194 


DENTAL  AND  ORAL  RADIOGRAPHY 


CHAPTER  I 

INTRODUCTION 

AVhen  AVilliam  Conrad  Roentgen  announced  to  the 
world  the  discovery  of  a  new  and  hitherto  unsuspected 
form  of  energy,  he  called  it  the  x-ray,  but  the  scientific 
world  has  for  the  most  part  seen  fit  to  designate  it  the 
"roentgen  ray"  in  honor  of  the  discoverer.  Roentgen- 
ology is,  therefore,  defined  as  ''the  study  and  practice  of 
the  roentgen  ray  as  it  applies  to  medicine  and  surgery/' 

For  purposes  of  study,  roentgenology  may  be  divided 
into  two  distinct  fields,  depending  upon  the  purpose  for 
which  the  roentgen  ray  is  to  be  utilized.  In  the  first, 
which  is  the  one  enlisting  the  interest  of  dentists,  it  is 
used  for  the  production  of  shadow  pictures  or  radio- 
grams. In  other  words,  it  embraces  what  is  commonly 
called  the  ''field  of  radiography/'  or  "roentgenog- 
raphy." 

The  other  branch  mentioned  includes  the  use  of  the 
roentgen  ray  for  therapeutic  purposes,  and  is  known 
as  "radiotherapy/'  or  "roentgenotherapy."  With  this 
field,  the  dentist  is  happily  not  directly  concerned,  and, 
therefore,  his  responsibilities  are  not  so  great  as  the 
medical  roentgenologist. 

Of  the  various  collateral  sciences  of  medicine,  there  is 
perhaps  no  other  which  has  developed  as  rapidly,  or 
which  has  assumed  a  more  important  bearing  in  many 
branches  of  practice  as  has  the  science  of  roentgenology. 
This  was  no  doubt  due  to  the  fact  that  the  more  progres- 

17 


18  DENTAL  AND   ORAL   RADIOGKAPHY 

sive  members  of  the  medical  and  dental  professions 
were  quick  to  realize  its  possibilities  and  adopted  it  so 
universally  that  a  great  stimulus  was  given  to  its  per- 
fection and  development,  with  the  result  that  although 
but  a  comparatively  short  time  has  elapsed  since  its  dis- 
covery, this  branch  has  been  evolved  to  the  state  where 
it  can  now  be  regarded  broadly  speaking  in  the  light  of 
an  exact  science. 

In  spite  of  this  fact,  there  is  still  apparent  in  some 
quarters  a  great  degree  of  misconception  as  to  the  re- 
sponsibilities of  one  who  is  to  actively  engage  in  this 
work.  This  is  evident  by  the  influx  into  this  field  of  a 
large  number  of  the  laity  who  in  spite  of  the  fact  that 
they  are  without  medical  or  dental  training  or  experi- 
ence, have  for  purely  commercial  reasons  attempted  to 
establish  themselves  as  radiographers. 

To  such,  this  field  of  labor  apparently  presents  allur- 
ing possibilities  as  is  evident  by  the  numerous  instances 
where  lajanen  have  engaged  in  such  work  without  ade- 
quate preparation.  To  these,  the  reward  of  bitter  dis- 
appointment must  eventually  come  for  the  time  is  fast 
approaching  when  the  intelligent  public  will  realize  the 
grave  responsibilities  encumbent  upon  the  ^'dispenser  of 
x-rays"  and  will  demand  expert  service.  It  is  encumbent 
upon  the  dentist  therefore,  not  to  be  satisfied  with  the 
acquiring  of  a  ''partial  knowledge"  of  the  subject,  which 
at  best  can  only  carry  one  half-way  upon  the  journey  of 
success,  but  he  should  early  come  to  a  realization  that 
the  practice  of  roentgenology  or  any  of  its  branches  re- 
quires much  more  than  a  mere  training  in  the  mechanics 
of  the  x-ray  laborator}^ 

Undoubtedly,  many  a  man  has,  in  the  contemplation  of 
x-ray  apparatus  for  his  office,  given  serious  thought  to 
the  type  of  equipment  which  he  wished  to  install,  and  has 
assumed  that  with  a  modern  laboratory,  he  would  be  in 


INTRODUCTION  19 

a  position  to  render  the  best  of  service.  Such  a  mis- 
gnided  individual  all  too  soon  learns  that  a  very  large 
part  of  the  battle  lies  within  himself,  and  if  his  own 
knowledge  is  deficient,  the  finest  equipment  in  the  world 
will  not  make  him  a  roentgenologist.  It  is  important, 
therefore,  that  those  who  contemplate  any  indulgence  in 
this  field  should  not  underestimate  the  task  that  con- 
fronts them  or  consider  lightly  the  responsibilities  it 
entails. 

In  addition  to  becoming  familiar  with  the  electro- 
physics  of  x-ray  laboratory  equipment,  its  practical  ap- 
plication in  his  chosen  field,  the  dangers  which  surround 
it  if  improperly  used,  one  should  realize  that  the  real 
practice  of  roentgenology  begins  when  the  x-ray  picture, 
or  radiogram,  has  been  produced.  It  is  quite  impos- 
sible for  such  an  image  to  be  of  value  unless  the  roent- 
genologist is  thoroughly  familiar  with  the  anatomy,  phys- 
iology, and  pathology  of  the  field,  under  examination; 
and  even  these  qualifications  are  not  adequate  unless 
backed  up  by  practical  clinical  experience. 

For  those  who  can  qualify,  it  will  be  found  that  there 
is  a  real  field  and  a  rare  opportunity  for  useful  service. 
It  will  also  be  found  that  everj^one  who  engages  in  this 
work  Avill  receive  just  that  amount  of  recognition  and 
respect  from  his  colleagues  to  which  his  abilities  entitle 
him,  for,  as  already  alluded  to,  this  is  an  exacting  voca- 
tion and  is  no  fit  place  for  the  mediocre  or  ill  prepared. 

At  the  very  outset  the  beginner  should  become  familiar 
with  the  terminology  of  the  subject,  and  cultivate  the 
habit  of  using  terms  correctly.  Failure  to  do  this  soon 
stamps  one  as  a  presumptuous  amateur.  For  instance, 
instead  of  using  the  term  ''x-ray  picture,"  such  an  image 
should  always  be  spoken  of  as  a  ^'radiogram/'  or  as  a 
''roentgenogram,"  or  if  the  area  involved  is  but  of  one 


20  DEKTAL  AND  ORAL  RADIOGRAPHY 

or  more  teeth  and  their  investing  tissues,  the  term 
"odontogram"  might  be  appHed. 

The  physician  or  the  dentist  maintaining  an  x-ray 
laboratory  should  not  be  called  an  ''x-ray  specialist," 
but  should  be  spoken  of  as  a  '^ medical  or  a  dental  roent- 
genologist." A  dental  roentgenologist  may  also  be  prop- 
erly spoken  of  as  a  radiodontist,  or  the  broader  term 
''oral  radiographer"  may  be  used. 

Not  infrequently,  we  hear  physicians  or  dentists  speak- 
ing of  a  dental  radiogram  as  a  "dental  x-ray."  Such 
an  expression  should  be  avoided  as  it  is  crude  and  devoid 
of  any  real  meaning. 

It  is  thought  by  some  terminologists  that  in  addition  to 
always  speaking  of  the  x-ray  as  the  roentgen  ray,  in  honor 
of  the  man  who  discovered  it,  we  should  include  the  name 
roentgen  in  every  descriptive  word  connected  with  the 
work.  To  such,  the  term  "radiograph"  (verb)  and 
"radiogram"  (noun)  will  doubtless  appear  improper, 
but  the  author  feels  justified  in  continuing  their  use,  as 
these  words  are  thoroughly  descriptive  and  less  cum- 
bersome than  ''roentgenograph"  and  "roentgenogram." 
For  the  same  reason,  the  term  "radiography"  is  pre- 
ferred rather  than  "roentgenography"  to  designate  the 
art  of  making  radiograms. 

To  some,  the  term  "radiogram"  seems  improper,  the 
claim  being  made  that  this  term  is  used  in  Wireless  ter- 
minology to  imply  a  Marconigram.  However,  there 
should  be  little  chance  for  confusion  as  the  subjects  are 
sufficiently  segregated  so  that  there  is  small  chance  for 
misinterpretation  of  the  word. 

Briefly  summarized,  the  following  roentgen  terminol- 
ogy will  be  found  to  be  quite  adequate : 

Roentgen  ray,  or  A  phenomenon  in  physics  discovered  by 

X-ray:  William  Conrad  Roentgen. 


INTRODUCTION 


21 


The  study  and  practice  of  the  roentgen 
ray  as  applied  to  medicine  and  surgery. 

One  skilled  in  roentgenology,  or  radi- 
ology. 

One  skilled  in  use  of  the  roentgen  lay  in 
making  roentgenograms  or  radiograms. 

One  skilled  in  the  art  of  making  roent- 
genograms or  radiograms  of  the  dental 
and  oral  structures  and  interpreting 
the  findings. 

The  shadow  picture  produced  by  the  x- 
ray  upon  the  photographic  emulsion. 

The  shadow  picture  of  teeth  and  their 
investing  tissues  produced  by  the  x-ray 
upon  the  photographic  emulsion. 

(Verb.)  To  make  a  roentgenogram,  or 
radiogram. 

The  art  of  making  roentgenograms,  or 
radiograms. 

The  art  of  making  roentgenograms  or 
radiograms  of  the  dental  and  oral 
structures. 

Treatment  by  the  application  of  the 
roentgen  ray. 

Skin  reaction  due  to  too  strong  or  too 
often  repeated  application  of  the  roent- 
gen ray. 
Roentgenographic  examination,  or    The  examination  and  study  of  the  shadow 


Roentgenology,  or 
Radiology :  * 

Roentgenologist,  or 
Radiologist :  * 
Radiographer : 

Radiodontist :  t 


Roentgenogram,  or 
Radiogram : 

Odontogram : 


Roentgenograph,  or 
Radiograph : 

Roentgenography,  or 
Radiography : 

Radiodontia :  i 


Roentgenotherapy,  or 
Radiotherapy :  * 
Roentgen  dermatitis,  or 
X-ray  dermatitis: 


Radiographic  examination : 

Roentgen  diagnosis,  or 
X-ray  diagnosis: 
Pathoroentgenography,  or 
Pathoradiography :  t 


pictures  produced  by  the  x-ray  upon 
the  photographic  emulsion. 
Diagnosis  by  aid  of  the  roentgen  ray. 

The  study  of  pathologic  lesions  as  re- 
vealed by  the  radiogram,  or  roentgeno- 
gram; it  implies  and  renders  impera- 
tive a  knowledge  of  the  pathology  and 
of  the  interpretation  of  normal  and 
abnormal  tissue  densities  as  recorded 
in  the  radiogram. 

*The  term  is  rather  confusing,  as  it  could  also  refer  to  the  practice  and  therapy 
of  radium  or  other  radiotherapeutic  agents. 
tTerms  suggested  by  Dr.  Julio  Endelman. 
ITerms  suggested  by  Dr.  Howard  R.  Raper. 


22  DENTAL  AND  ORAL  RADIOGRAPHY 

Eadiopacity:§  Implying  an  increased  resistance  of  the 

tissues  to  the  penetration  of  the  rays. 

Eadiolucence:§  A  decreased  resistance  of  the  tissues  to 

the  penetration  of  the  x-rays. 

Roentgenize :  To  apply  the  roentgen  ray. 

Roentgenization :  The  application  of  the  roentgen  ray. 

Roentgenism:  The  untoward  effect  of  the  roentgen  ray. 

Some  writers  add  other  descriptive  terms  to  the  fore- 
going list,  but  the  author  feels  that  a  terminology  should 
be  just  as  brief  as  is  consistent  with  adequate  descrip- 
tion ;  hence,  several  terms  appearing  in  current  literature 
on  different  phases  of  roentgenology  have  been  omitted. 


§Terms  suggested  by   Dr.    R.    Ottolengui. 


CHAPTER  II 

THE  NATURE  OF  THE  X-RAY  AND  ITS 
DISCOVERY 

In  order  to  gain  an  intelligent  conception  of  the  x- 
ray,  it  is  quite  necessary  that  the  student  start  with 
a  consideration  of  certain  phases  of  electrophysics,  and 
radiant  energy,  or  in  fact  the  very  foundation  of  matter 
itself. 

According  to  the  most  plausible  theories  and  beliefs, 
all  matter  is  suspended  or  contained  in  the  medium 
known  as  ether,  which  is  an  elastic  medium  filling  all 
space,  interatomic  and  interelectronic,  as  well  as  all 
other  space  of  which  we  have  any  knowledge. 

Furthermore,  many  facts  brought  out  by  the  close 
study  of  chemistry  and  physics  seem  to  justify  the  be- 
lief that  all  substances  of  matter  are  composed  of  mi- 
nute particles  called  ''molecules,"  and  that  each  mole- 
cule is  made  up  of  two  or  more  elements  called  '  *  atoms, ' ' 
while  these  atoms  are  also  further  divided  in  particles 
known  as  electrons. 

These  electrons,  or  units  of  matter,  are  never  still,  but 
are  in  a  constant  state  of  motion  or  vibration,  each  sub- 
stance having  its  own  specific  atom  and  the  electrons  of 
such  atoms  having  their  own  rate  of  vibration. 

The  vibration  of  these  electrons  produces  disturbances 
in  the  ether  know  as  * '  ether  waves ' '  which  vary  in  length 
according  to  the  rate  at  which  electrons  are  vibrating. 
If  the  rate  of  vibration  of  the  electrons  be  changed  or 
disturbed,  there  is  a  change  in  the  ether  waves,  resulting 
in  a  corresponding  change  in  the  phenomenon  produced. 

If  this  theory  of  matter  is  correct,  as  the  evidence  of 

23 


24  DENTAL   AND   ORAL   RADIOGRAPHY 

modern  science  would  lead  us  to  believe,  all  matter  then 
is  made  up  of  the  same  constituents,  and  its  various  forms 
are  determined,  not  by  any  essential  difference  of  com- 
position, but  by  the  number,  arrangement  and  amount 
of  motion  of  the  ultimate  particles  making  up  the  atom. 

All  this  has  a  practical  significance  to  us  in  under- 
standing the  phenomenon  which  we  call  the  x-ray.  As 
stated  before,  it  is  known  that  a  certain  rate  of  vibra- 
tion of  electrons  will  produce  other  waves  resulting  in  a 
definite  phenomenon,  while  a  change  in  this  rate  will 
produce  an  entirely  different  phenomenon.  For  instance, 
a  slow  rate  of  vibration  (75,000,000  per  second)  produces 
what  are  known  as  electromagnetic  waves.  A  little 
higher  up  the  scale  where  the  electrons  are  made  to  vi- 
brate faster,  heat  waves  appear.  Another  increase,  and 
light  waves  appear.  If  we  continue  to  accelerate  the 
rate  of  vibrations  of  the  electrons,  there  will  be  pro- 
duced successively  ultra-violet,  or  Finsen  rays ;  then  cath- 
ode, or  radium,  rays,  and  finally  the  x-ray. 

It  will  then  be  seen  that  the  x-rays  are  produced  as  the 
result  of  the  most  rapid  rate  of  vibration  of  which  we 
have  any  knowledge.  In  the  laboratory  this  phenomenon 
is  produced  by  the  sudden  stopping  of  a  stream  of  rapidly 
moving  free  electrons  in  a  vacuum  tube  which  has  been 
exhausted  to  one  millionth  of  an  atmosphere. 

The  x-ray,  therefore,  may  he  defined  as  that  form  of 
radiation  ivhich  emanates  from  a  highly  exhausted  tube 
ivhen  an  electric  current  of  high  tension  is  passed  through 
the  tube.  The  object  of  the  vacuum  tube  is  to  establish 
a  medium  in  which  all  source  of  resistance  is  removed, 
so  that  the  electric  current  may  excite  the  exquisitely 
rapid  vibrations  necessary  to  produce  the  phenomenon 
desired,  the  electric  current  being  the  source  of  excita- 
tion. 

The  radiation  thus  produced  gives  neither  heat  nor 


NATURE   OF   X-EAY   Al^D   ITS   DISCOVERY  25 

light,  nor  can  it  be  deflected,  reflected,  or  polarized.  In 
fact,  it  can  only  be  recognized  by  its  effect  upon  the 
photographic  plate  and  upon  such  chemicals  as  willem- 
ite,  calcium,  and  tungstate,  which  fluoresce  or  glow  un- 
der its  influence. 

The  Discovery  of  the  X-ray 

The  x-ray  was  discovered  in  1895  by  William  Conrad 
Roentgen,  Professor  of  Physics,  at  the  Royal  University 


Fig.    1. — William   Conrad    Roentgen. 


of  Wiirzburg,  in  Germany.  This  discovery,  marking  as 
it  did,  a  distinct  epoch  in  the  science  of  medicine,  was  re- 
ceived by  the  world  with  incredulity  and  amazement,  for 


26 


DENTAL  AND   ORAL  RADIOGRAPHY 


its  reported  possibilities  savored  almost  of  the  oc„ 
"A  new  ray  had  been  discovered  by  means  of 
was  possible  to  look  through  opaque  substances.'" 

While  it  fell  to  the  lot  of  Professor  Koentgen  to  make 
this  discovery,  there  is  no  doubt  but  that  other  experi- 
menters in  the  field  of  physics,  unconsciously  produced 


Fig.  2. — Michael  Faraday, 

this  same  ray.  In  fact,  its  discovery  was  made  possible 
by  the  work  of  other  scientists  who  preceded  Koentgen 
and  laid  the  foundation  for  its  advent. 

Of  these,  Michael  Faraday  was  the  pioneer.  In  1831 
he  discovered  electro-magnetic  induction,  which  made 
possible  the  induction  coil  and  the  other  electric  machines 


NATUKE   OF   X-RAY  AND   ITS   DISCOVERY 


27 


.^dd  1x0  generate  currents  of  great  potential.    As  early 
IB  conducted  a  series  of  experiments  to  deter- 
mine the  effect  of  electric  discharges  upon  rarified  gases, 
and  invented  the  terms  "anode"  and  "cathode"  for 
positive  and  negative  electrodes. 

In  1857  Geissler  constructed  the  first  vacuum  tubes 
and  it  was  noted  at  this  time  that  an  electric  discharge 
passed  through  these  tubes  would  produce  a  peculiar 


Fig.   3. — Sir  William   Crookes. 

glow  or  phosphorescence,  the  coloring  of  which  depended 
upon  the  character  of  the  rarefied  gas  contained  in  the 
tube.  This  phenomenon  became  known  as  "fluores- 
cence." 

A  few  years  later  (1860)  Professor  Hittorf,  a  cele- 
brated physicist  of  Miinster,  conceived  the  idea  of  ex- 
hausting the  Geissler  tube  to  a  higher  degree  of  vacuum 
and  found  as  a  result  an  increased  resistance  to  the  pass- 


28  DENTAL   AND   ORAL   RADIOGRAPHY 

ing  of  the  electric  discharge,  and  that  the  color  of  the 
rarefied  gases  under  fluorescence,  varied  with  the  degree 
of  rarefication.  He  also  discovered  another  fact  which 
was  to  have  an  important  bearing  upon  the  work  of  later 
experimenters,  and  that  was  that  the  luminous  discharge 
in  a  Geissler  tube  could  he  deflected  hy  a  magnet. 

The  important  work  of  these  early  experimenters  was 
followed  later  (1878)  by  Sir  William  Crookes,  who  suc- 


Fig.  4. — Heinrich  Hertz. 

ceeded  in  constructing  a  more  perfect  vacuum  tube,  that 
is,  one  that  could  be  exhausted  to  a  much  higher  degree 
of  vacuum.  "With  these  improved  tubes,  Crookes  discov- 
ered that  with  a  sufficiently  high  vacuum  the  luminous 
glow  within  the  tube  disappeared,  and  demonstrated  that 
within  it  there  was  a  rectilinear  radiation  from  the 
cathode,  which  he  conceived  as  being  a  projection  of  par- 
ticles of  highly  attenuated  gas  at  exceedingly  high  veloc- 


NATURE   OF   X-RAY   AND   ITS   DISCOVERY  29 

ity.  To  this  radiation  he  gave  the  name  ' '  cathode  rays, ' ' 
and  because  of  the  peculiar  behavior  of  gas  in  this  ex- 
ceedingly rarefied  state,  he  concluded  that  it  was  as  dif- 
ferent from  gas  in  its  properties  as  ordinary  air  or  gas 
is  different  from  a  liquid.  He  found  that  the  impact  of 
the  cathode  rays  against  the  wall  of  the  tube  would  pro- 
duce within  it  a  greenish  "phosphorescence"  or  '^fluores- 
cence" and  an  increase  in  temperature;  also  that  these 
rays  could  be  intercepted  by  metallic  plates  within  the 
tube.  By  concentrating  the  rays  at  the  focus  of  a  con- 
cave cathode,  he  was  able  to  produce  a  brilliant  fluores- 
cence and  a  very  high  temperature,  both  at  the  walls  of 
the  tube  and  in  various  substances  within  it.  Without 
doubt,  Sir  William  CrooJces  unconsciously  produced  the 
x-ray  in  the  course  of  these  experiments. 

In  1892  Professor  Heinrich  Hertz  discovered  that 
cathode  rays  would  penetrate  gold  leaf  and  other  thin 
sheets  of  metal  placed  within  the  tube.  Soon  after  this 
discovery.  Hertz  died,  and  his  experiments  were  con- 
tinued by  his  assistant,  Lenard,  who  was  able  to  demon- 
strate that  many  of  the  phenomena  of  the  cathode  rays 
could  be  observed  outside  of  the  Crookes  tube.  By  clos- 
ing a  vacuum  tube  at  the  end  opposite  the  cathode  with 
a  thin  sheet  of  aluminum,  he  demonstrated  that  a  radia- 
tion proceeded  through  or  from  the  aluminum  walls  of 
the  tube  which  would  pass  through  many  substances 
opaque  to  ordinary  light,  and  after  passing  through  such 
substances,  it  would  excite  fluorescence  in  crystals  of  ba- 
rium platino-cyanide,  and  would  affect  sensitive  photo- 
graphic plates  in  much  the  same  manner  as  ordinary 
light.  Lenard  considered  that  all  these  phenomena  were 
due  to  the  cathode  rays  alone,  although  in  the  light  of 
our  present  knowledge,  there  is  no  doubt  tlmt,  not  only 
in  his  experiments,  but  in  those  of  Crookes,  Hertz,  and 
other  investigators,  x-rays  were  produced.     However, 


30  DENTAL   AND   ORAL   RADIOGRAPHY 

they  were  not  recognized  as  such  until  1895  when  Pro- 
fessor Roentgen  startled  the  world  hy  the  armouncenient 
of  his  discovery. 

Upon  the  memorable  day  of  his  discovery,  Professor 
Koentgen  was  duplicating  one  of  Lenard's  experiments 
in  the  laboratory  of  the  Wiirzburg  University.  The  ex- 
periment consisted  of  passing  an  electric  current  through 
a  Crookes  tube  covered  with  black  cardboard,  to  test  its 
fluorescence  upon  a  piece  of  cardboard  coated  with  ba- 
rium platino-cyanide.  A  fresh  specimen  of  this  chemical 
had  been  prepared  and  spread  upon  the  cardboard  which 
was  placed  against  the  wall  on  the  opposite  side  of  the 
room  to  dry.  The  room  was  darkened  and  the  current 
was  passing  through  the  tube,  when  to  his  amazement, 
Eoentgen  noticed  that  the  chemically  covered  cardboard 
on  the  other  side  of  the  room  was  glowing  with  a  wierd 
fluorescence.  He  approached  the  cardboard,  and  in  doing 
so,  passed  between  it  and  the  Crookes  tube,  and  beheld 
his  shadow  upon  the  cardboard.  Picking  up  a  book,  he 
held  it  in  front  of  the  screen  and  noticed  that  it  also  cast 
a  shadow.  He  then  discovered  that  the  luminous  glow  or 
fluorescence  on  the  cardboard  appeared  and  disappeared 
with  the  turning  on  and  off  of  the  current.  With  the 
tube  operating,  he  picked  up  the  cardboard,  and  while 
examimng  it,  noticed  the  shadow  of  his  hand  on  its 
surface,  the  hones  appearing  much  darker  than  the  soft 
parts  of  the  hand.  He  also  found  that  the  fluorescence 
was  produced  in  the  cardboard  regardless  of  whether  the 
chemically  coated  side  was  turned  toward  or  away  from 
the  Crookes  tube,  showing  that  the  rays  had  the  power 
to  penetrate  substances  at  a  distance  from  the  tube. 

Further  investigation  proved  that  the  radiation  pro- 
ducing these  phenomena  emanated  from  the  point  of  im- 
pact of  the  cathode  rays  against  the  glass  wall  of  the 
Crookes  tube;   that  nearly  all  substances  were  trans- 


NATUKE   OF   X-RAY   AND   ITS   DISCOVERY  31 

parent  to  it,  although  in  widely  different  degrees,  varying 
roughly  with  their  density ;  that  the  radiation  was  recti- 
linear; that  it  could  not  be  refracted,  reflected,  or  de- 
flected by  a  magnet.  Hence  it  was  plain  to  Roentgen  that 
these  rays  were  quite  different  from  the  cathode  rays  of 
Crookes,  Hertz,  or  Lenard. 

Using  photographic  plates  wrapped  in  black  paper  to 
protect  them  from  ordinary  light,  he  obtained  with  these 
new  rays  shadow  pictures  of  metallic  objects  in  a  wooden 
box,  and  of  the  bones  of  the  hand. 

He  continued  his  experiments  both  with  the  fluorescent 
screen  and  the  photographic  plate,  and  in  December, 
1895,  communicated  his  discovery  to  the  Physico-Medical 
Society  of  Wurzburg.  Being  unable  to  determine  the 
exact  nature  of  this  new  ray  other  than  classing  the 
phenomenon  as  longitudinal  vibrations  of  ether.  Roent- 
gen called  it  the  x-ray,  the  letter  ^'x"  representing  the 
unknown  in  the  mathematical  formula.  Even  today  the 
exact  nature  of  the  rays  has  not  been  determined,  al- 
though the  concensus  of  opinion  seems  to  be  that  they 
are  violent  ether  pulses  set  up  by  the  sudden  stoppage 
of  the  cathode  rays  as  they  strike  upon  the  walls  of  the 
tube  or  upon  any  intervening  obstruction.  If  this  theory 
be  correct,  x-rays  are  of  the  same  general  nature  as  light 
waves,  but  of  such  short  wave  length  that  they  lie  out- 
side the  visible  spectrum. 


CHAPTER  III 

HIGH  TENSION  ELECTRIC  CURRENTS- 
MAGNETISM— ELECTROMAGNETIC 
INDUCTION 

High  Tension  Electric  Currents 

As  stated  previously,  the  x-ray  is  produced  when  an 
electric  current  of  high  tension  is  passed  through  a  vac- 
uum tube.  Therefore,  let  us  consider  the  character  of 
this  current  and  the  means  employed  to  produce  it. 

There  are  several  kinds  of  electric  currents,  but  of 
these  we  need  concern  ourselves  only  with  two — the 
direct  current,  commonly  designated  by  the  abbreviation 
D.C. ;  and  the  alternating  current,  designated  as  A.C. 

The  direct  current  is  one  in  which  the  electricity  flows 
along  a  conductor  in  one  direction  at  a  uniform  rate  of 
pressure,  while  the  alternating  current  flows  along  a  con- 
ductor first  in  one  direction,  then  reverses  and  flows  in 
the  opposite  direction,  these  changes  taking  place  with 
great  rapidity  (50  to  120  per  second).  Such  a  current  in 
making  these  changes  is  said  to  have  completed  a  cycle, 
and  its  frequency  is  designated  by  the  number  of  alter- 
nations which  occur  each  second. 

A  high  tension  current  is  one  which  has  high  voltage, 
or,  as  it  is  expressed  in  electrical  terms,  has  great  elec- 
tromotive force,  or  pressure. 

The  Volt  is  defined  as  the  unit  of  electromotive  force, 
and  is  analogous  to  the  pressure  caused  by  a  difference 
in  level  of  two  bodies  of  water  connected  by  a  pipe — the 
pressure  tends  to  force  the  water  through  the  pipe  and 

32 


HIGH   TENSION   ELECTRIC    CURRENTS  33 

the  electromotive  force  or  voltage  tends  to  cause  the  elec- 
tric current  to  flow  along  a  conductor. 

The  Ampere  is  the  unit  of  current  strength,  or  in  other  ^ 
words,  the  amount  of  current  passing  a  given  point  on  a 
conductor  in  a  given  time.  If  we  again  use  the  analogy 
of  the  two  bodies  of  water  at  different  levels  connected 
by  a  pipe,  it  would  be  the  amount  of  water  which  could 
pass  through  the  pipe  in  a  given  time. 

The  Ohm  is  the  unit  of  resistance.  Just  as  the  water 
in  flowing  through  a  pipe  is  resisted  somewhat  in  its  pas- 
sage by  the  friction  offered  by  the  surface  of  the  pipe, 
or  by  the  limited  capacity  of  the  pipe,  so,  likewise,  the 
electric  current  is  resisted  in  varying  degrees  in  its  pas- 
sage along  a  conductor,  the  degree  of  resistance  depend- 
ing upon  the  degree  of  conductivity  of  the  material  used 
as  the  conductor,  its  length,  cross  section,  etc. 

The  Watt  is  the  unit  of  electromotive  poiver  or  the 
ability  of  a  current  to  do  work.  The  wattage  of  a  cur- 
rent is  determined  by  the  voltage,  or  pressure,  and  the 
amperage  or  quantity,  the  wattage  of  a  given  current  be- 
ing determined  by  multiplying  the  voltage  by  the  am- 
perage. 

From  the  foregoing,  then,  we  see  that  the  character  of 
an  electric  current  is  determined  by  several  factors,  all 
of  which  must  be  taken  into  consideration. 

If  we  wish  to  know  the  strength  of  a  given  current,  we 
have  but  to  remember  this  strength  will  depend  upon  the 
pressure  or  electromotive  force  and  the  resistance  of- 
fered by  the  conductor  through  which  the  current  is  pas- 
sing, just  as  the  strength  of  a  stream  of  water  flowing 
from  a  tank  would  depend  upon  the  pressure  and  the  size 
of  the  pipe  carrying  the  water.  In  other  words,  the 
strength  of  the  electric  current  equals  the  pressure  di- 
vided hy  the  resistance.  Reducing  this  to  an  equation 
we  have — 


34  DENTAL   AND   ORAL   RADIOGRAPHY 

volts                          E.M.F. 
Amperes  =    ^^^^^g    or  C  equals  -^ 

This  is  known  as  ''Ohm's  Law"  and  is  one  of  the  fun- 
damental laws  upon  which  electrical  science  is  based. 
This  important  law  has  two  other  forms  which  make  it 
possible  to  learn  the  relationship  and  amount  of  any  of 
these  three  units,  provided  two  are  known.  For  instance, 
by  transposing  the  formula  of  Ohm's  law,  we  have — 

Volts  =  amperes  x  ohms,  or  E.M.F.  =  C  x  R. 

If  we  wish  to  determine  the  resistance  offered  by  a 
given  conductor,  we  apply  the  formula  as  follows : 

E.M.F.  E.M.F. 

Resistance  = or  R  = 7i 

amperage  G 

As  stated  before,  the  current  which  is  passed  through 
the  vacuum  tube  to  generate  the  x-rays  must  be  a  cur- 
rent of  high  tension,  or  great  pressure ;  or,  expressed  in 
the  terms  of  the  units  just  described,  it  must  have  very 
high  voltage.  The  ordinary  lighting  current  of  110  volts 
is  inadequate,  as  this  current  is  of  far  too  low  potential 
to  pass  through  the  tube,  as  the  vacuum  offers  great  re- 
sistance, a  resistance  which  to  the  ordinary  current 
amounts  to  an  absolute  nonconductor.  We  are  obliged, 
therefore,  to  make  use  of  some  means  which  will  pro- 
duce a  current  of  great  voltage,  a  current,  we  will  say, 
of  at  least  75,000  to  150,000  volts. 

To  do  this,  we  must  make  use  of  one  of  the  electric 
machines  which  can  generate  such  a  current  by  utilizing 
the  principle  of  electromagnetic  induction.  Lest  the  stu- 
dent become  confused,  we  will  first  review  very  briefly 
some  of  the  elementary  principles  of  electromagnetism 
and  its  relation  to  the  production  of  the  high  tension  cur- 
rent necessary  in  x-ray  production. 


HIGH   TENSION   ELECTRIC    CURRENTS  35 

Magnetism 

Magnetism  is  the  term  applied  to  substances  which 
have  the  property  of  attracting  small  pieces  of  iron.  A 
material  possessing  this  property  was  first  found  by  the 
ancients  at  Magnesia,  in  Asia  Minor,  from  which  fact 
arose  the  name  magnet. 

The  natural  magnet  is  an  oxide  of  iron  and  is  also 
called  the  lodestone.  Artificial  magnets  can  be  made  by 
rubbing  a  bar  of  hard  steel  with  a  lodestone,  or  with  an- 
other artificial  magnet,  or  by  means  of  an  electric  cur- 
rent. Artificial  magnets  acquire  the  same  magnetic 
properties  which  the  lodestone  or  natural  magnet  pos- 
sesses except  that  they  acquire  them  to  a  much  greater 
extent,  and  are,  therefore,  always  used  in  preference  to 
natural  magnets. 

In  addition  to  the  property  of  attracting  small  pieces 
of  iron,  magnets  have  other  characteristics  worthy  of 
mention,  such  as  polarity,  or  the  property  of  assuming, 
when  suspended  and  perfectly  free  to  move,  a  north  and 
south  position.  The  compass  is  quoted  as  a  familiar 
example. 

At  the  ends  of  a  magnet,  or  in  other  words  at  its  poles, 
the  greatest  power  or  attraction  exists.  This  is  easily 
illustrated  by  placing  one  end  of  an  ordinary  magnet  in 
some  iron  filings  and  withdrawing  it.  The  filings  will 
cling  to  it  in  great  numbers,  as  they  will  likewise  do  to 
the  other  end  of  the  same  magnet  if  it  too  be  placed  in 
the  filings.  The  middle  of  the  magnet  (or  that  portion 
midway  between  the  two  poles),  however,  does  not  pos- 
sess this  property;  but  as  the  ends  are  approached,  the 
attraction  increases  until  the  poles  are  reached,  where  it 
reaches  the  maximum. 

In  observing  the  action  of  the  two  poles  of  a  magnet 
in  attracting  the  iron  filings,  no  particular  difference  is 


36 


DENTAL  AND   ORAL   RADIOGRAPHY 


observed.  They  both  attract  the  iron  filings.  There  is  a 
difference,  however,  which  may  be  shown  by  experiment- 
ing with  two  magnets,  one  of  which  should  be  suspended 
at  its  center  like  an  ordinary  compass,  while  the  other  is 
held  in  the  hand.  If  the  north  pole  of  the  magnet  held 
in  the  hand  is  moved  near  the  north  pole  of  the  sus- 
pended magnet,  they  tvill  repel  each  other.  Likewise  if 
their  south  poles  are  approached,  they  will  repel  each 
other.  But  if  the  north  pole  of  one  be  placed  near  the 
south  pole  of  the  other,  they  will  attract  each  other. 


Fig.  5. — The  action  of  iron  filings  in  forming  definite  curved  lines  about  an  or- 
dinary bar  magnet  indicates  that  the  magnetic  field  exerts  its  influence  in  certain 
definite  directions  which  are  called   "the  magnetic  lines  of  force." 


This  shows  that  like  poles  repel  each  other,  while  unlike 
poles  attract  each  other. 

The  space  surrounding  a  magnet  which  is  subject  to 
its  influence  is  known  as  its  magnetic  field.  The  presence 
of  this  magnetic  field  is  easily  demonstrated  by  placing  a 
magnet  under  a  sheet  of  paper  upon  which  iron  filings 
have  been  evenly  spread.  By  tapping  the  paper  lightly, 
the  filings  will  form  into  a  series  of  curved  lines  extend- 
ing from  one  pole  of  the  magnet  to  the  other  pole,  as  il- 
lustrated in  Fig.  5.     The  formation  of  these  definite 


HIGH   TENSION"   ELECTRIC    CURRENTS 


37 


curves  indicates  that  the  magnetic  field  exerts  its  influ- 
ence in  certain  definite  directions  which  are  called  the 
lines  of  magnetic  force.  These  lines  of  force  start  at  one 
pole  of  the  magnet,  pass  in  curved  lines  around  to  the 
opposite  pole,  where  they  re-enter  and  pass  on  through 
the  magnet  again,  so  that  if  any  line  is  followed  through 
its  entire  length,  one  will  eventually  come  back  to  the 
starting  point,  as  shown  in  Fig.  6. 

It  is  by  virtue  of  its  magnetic  field,  that  a  magnet  has 
the  power  of  attracting  pieces  of  iron.    "When  a  piece  of 


'II    /     "  ^ 
x\\\     /   / 


-.       \       \    \    S 


'//// 1 1  I 


1  '  \ 


y      / 


Fig.  6. — Diagrammatic  illustration  of  the  magnetic  lines  of  force. 


iron  is  brought  under  its  influence,  it  becomes  a  tem- 
porary magnet,  and  for  the  time  being  has  its  two  poles. 
If  the  north  pole  of  a  magnet  is  brought  close  to  a  piece 
of  iron,  a  south  pole  will  be  induced  in  the  iron  next  to 
this  north  pole,  and  a  north  pole  in  the  portion  farthest 
from  it.  The  attraction  is  then  exactly  similar  to  the  at- 
traction between  two  permanent  magnets  when  two  un- 
like poles  are  brought  together.  This  action  of  a  mag- 
net in  developing  magnetism  in  iron  placed  in  its 
magnetic  field  is  called  magnetic  induction. 

When  a  piece  of  iron  is  in  contact  with  a  magnet,  the 
attraction  is  greatest;  but  actual  contact  is  unnecessary 


38  DENTAL  AND   ORAL   RADIOGRAPHY 

to  magnetize  the  iron,  as  it  need  only  be  placed  ivithin 
the  magnetic  field,  or,  in  other  words,  within  the  mag- 
netic lines  of  force  of  the  magnet. 

Magnetism  may  be  induced  in  iron  in  another  way  not 
yet  described,  and  to  ns  this  is  of  great  importance.  If 
an  ordinary  electric  current  is  passed  through  a  coil  of 
wire,  the  coil  becomes  equivalent  to  a  magnet  and  is  sur- 
rounded by  a  magnetic  field  similar  to  that  of  a  bar  mag- 
net. Such  a  coil  of  wire  is  called  a  helix,  and  if  its 
length  is  many  times  its  diameter,  it  is  called  a  solenoid. 


/.<-- ^.-~-<N 


y  ^ 


N 


y 


/ 


Fig.    7. — Diagrammatic   illustration   of  the   magnetic   field  surrounding   a   coil    of   wire 
through  which  an  electric  current  is  passing. 

Since  a  solenoid  is  surrounded  by  a  magnetic  field  sim- 
ilar to  that  of  a  magnet  (see  Fig.  7)  it  follows  that  a 
solenoid  is  capable  of  magnetizing  pieces  of  soft  iron 
and  attracting  them  in  the  same  way  as  does  an  ordinary 
steel  magnet.  The  magnetic  field  of  a  solenoid  is 
strongest  within  its  windings  and  therefore  if  a  bar  of 
soft  iron  is  placed  within  the  coil,  the  bar  will  be  much 
more  strongly  magnetized  than  if  placed  in  any  other 
position  about  the  coil.  Such  a  coil  adapted  to  carry  a 
current  and  provided  with  a  soft  iron  bar  or  core  is 
called  an  electromagnet  (Fig.  8). 


HIGH    TENSION   ELECTRIC    CURRENTS  39 

In  order  to  permit  the  wire  to  be  closely  wound  and 
at  the  same  time  to  allow  the  current  to  pass  through 
each  turn,  the  wire  must  be  covered  with  insulation 
throughout  its  length.  It  should  also  be  remembered 
that  the  iron  core  imthin  the  solenoid  remains  a  magnet 
only  ivhile  the  current  is  passvng  through  the  coil,  as 
"only  electric  charges  in  motion  produce  magnetic 
effects." 

Electromagnets  are  much  more  powerful  than  ordinary- 
magnets  ;  that  is,  their  fields  have  much  greater  strength, 
for  the  field  of  the  electromagnet  is  equal  to  the  sum  of 


Fig.  8. — An  iron  bar  placed  within  the  windings  of  a  solenoid  is  subject  to  its   mag- 
netic  field   and   becomes   a   magnet. 

the  field  due  to  the  core,  plus  the  field  due  to  the  current 
passing  through  the  coil. 

Thus  far  we  have  discussed  the  fact  that  a  magnetic 
substance  in  the  field  of  an  ordinary  magnet,  or  a  con- 
ductor carrying  an  electric  current,  is  magnetized.  This 
phenomenon,  we  know,  is  due  to  magnetic  induction.  It 
is  also  a  fact  that  an  electric  current  may  he  induced  in 
a  conductor  by  causing  the  latter  to  move  through  a  mag- 
netic field.  It  makes  no  difference  whether  this  field 
comes  from  an  ordinary  magnet  or  from  an  electric 
charge  passing  through  a  conductor.    This  action  of  a 


40 


DENTAL  AND   ORAL   RADIOGRAPHY 


magnet  or  of  a  current  on  a  conductor  moved  in  its  field 
is  called  electromagnetic  induction. 

Principles  of  Electromagnetic  Induction 

If  the  ends  of  a  coil  of  wire  are  connected  with  a  gal- 
vanometer (Fig.  9)  and  the  coil  is  moved  down  over  an 
ordinary  magnet,  the  galvanometer  will  show  that  a  mo- 
mentary electric  current  has  passed  through  the  coil. 


Fig.   9. — A,   magnet  with  diagrammatic   illustration   of  "magnetic  lines  of   force"   sur- 
rounding it.    B  shows  a  coil  of  wire  connected  to  a  galvanometer,  C. 

The  current  continues  as  long  as  the  coil  is  in  motion, 
and  ceases  as  soon  as  the  coil  is  brought  to  rest.  If  the 
coil  is  withdrawn  from  the  magnet,  a  current  is  also  in- 
duced which  flows  in  an  opposite  direction  to  the  current 
which  was  induced  when  the  coil  was  carried  down  over 
the  magnet. 

These  induced  currents  are  produced  hy  the  field  sur- 
rounding the  magnet  moving  or  cutting  across  the  wires 
composing  the  coil.  If  a  current  is  passed  through  the 
coil,  it  creates  a  magnetic  field,  and,  on  the  other  hand. 


HIGH    TENSION"   ELECTRIC    CURRENTS 


41 


the  movement  of  a  magnetic  field  within  the  coil  produces 
a  current. 

As  a  solenoid  is  surrounded  by  a  magnetic  field  similar 
to  an  ordinary  bar  magnet,  it  follows  that  if  a  solenoid 
carrying  a  current  were  thrust  within  (Fig.  10)  another 
coil,  induced  currents  will  be  produced  in  the  latter. 
These  induced  currents,  as  in  the  case  where  the  magnet 
is  used,  only  flow  while  there  is  a  relative  movement  be- 
tween the  magnetic  field  and  the  conductor.    "When  the 


Fig.   10. — A,  battery  from  which  an   electric  current  is  passing  through  the  solenoid, 
B;  C,  large  coil  into  which  the  smaller  coil  B  is  passed;  D,  galvanometer. 

solenoid  is  passed  into  the  other  coil,  the  induced  cur- 
rent will  floAv  in  an  opposite  direction  to  the  current 
"flowing  in  the  solenoid,  and  upon  withdraiving  the  sole- 
noid, the  induced  current  will  flow  in  the  smne  direction 
as  the  current  in  the  solenoid. 

Suppose  the  two  coils  just  described  are  placed  one 
within  the  other  (there  being  no  current  passing)  and 
while  in  this  position  a  current  is  started  in  the  inner 
coil.  Upon  the  passage  of  the  current  in  the  inner  coil, 
a  momentary  current  is  induced  in  the  outer  coil,  just  the 


42  DENTAL   AND   ORAL   RADIOGRAPHY 

same  as  if  a  magnet  had  been  moved  within  it,  as  shown 
in  Fig.  9.  This  induced  current  remains  only  while  the 
current  in  the  inner  coil  is  increasing  in  value  from  zero 
to  its  normal  strength.  As  soon  as  this  normal  strength 
is  reached,  the  induced  current  ceases  to  flow.  Now  if 
the  circuit  of  the  inner  coil  is  broken  and  its  current 
ceases  to  flow,  at  this  instant  another  momentary  cur- 
rent is  induced  in  the  outer  coil,  which  flows  in  a  direc- 
tion opposite  to  the  current  which  was  induced  by  start- 
ing the  current.  These  two  induced  currents  created  by 
starting  and  stopping  the  primary  current,  or  in  other 
words,  by  "making"  and  "breaking"  the  current,  are 
not  of  equal  strength,  the  one  produced  by  the  ^^hreah" 
of  the  current  being  much  the  stronger. 

Such  an  instrument  arranged  with  one  coil  within  the 
other,  but  without  any  connection  between  the  two  coils, 
is  known  as  an  "^induction  coil."  The  inner  coil  which 
is  usually  supplied  with  an  iron  core,  is  known  as  the 
"primary  coil;"  and  the  outer  coil,  in  which  the  current 
is  induced,  is  known  as  the  "secondary  coil." 

Induced  currents  are  greatly  intensified  ivhen  soft  iron 
cores  are  placed  within  the  primary  coils,  as  the  cores 
become  magnets  and  increase  the  strength  of  the  field 
by  adding  largely  to  the  lines  of  force  therein. 

If  an  induction  coil  is  constructed  with  the  same  num- 
ber of  turns  of  wire  in  the  "secondary"  as  are  present 
in  the  "primary,"  the  current  induced  in  the  secondary 
will  be  exactly  equal  to  the  current  passed  through  the 
primary.  The  voltage  will  not  be  increased.  On  the 
other  hand,  if  the  secondary  contains  twice  as  many 
turns  as  the  primary,  the  induced  current  will  be  double 
the  voltage  of  the  primary,  as  each  turn  of  the  secondary 
induces  a  current  in  the  turns  directly  adjacent  to  it, 
which  must  be  added  to  the  current  induced  in  the  first 
layer  by  the  action  of  the  primary  current.    Therefore, 


HIGH    TENSION    ELECTRIC    CURRENTS  43 

it  should  be  apparent  that  as  we  increase  the  number  of 
turns  in  the  secondary,  we  increase  the  E.M.F.,  or  volt- 
age. This  increase  of  E.M.F.,  or  voltage,  is  due  to  the 
phenomena  of  "self-induction"  which  is  the  principle 
utilized  in  all  x-ray  machines  or  other  electrical  appara- 
tus used  to  ' '  step  up ' '  the  E.M.F.,  or  voltage. 


CHAPTER  IV 

X-RAY  MACHINES 

RHUMKORFF  OR  INDUCTION  COIL— TESLA 

OR  HIGH  FREQUENCY  COIL— INTERRUP- 

TERLESS  TRANSFORMER— STEP  UP 

TRANSFORMER  UNIT 

The  Rhumkorff  or  Induction  Coil 

The  Rhumliorff,  or  ''induction  coil,"  was  for  many 
years  the  most  popular  and  widely  used  type  of  x-ray 
machine.  AVhile  it  is  gradually  being  supplanted  by 
other  types,  many  are  still  in  use  and  for  this  reason 
a  description  of  its  principles  is  not  deemed  out  of  place. 
Furthermore,  a  knowledge  of  its  mechanism  cannot  but 
aid  in  understanding  the  other  types  of  apparatus. 

The  induction  coil  may  be  said  to  consist  of  two  princi- 
pal parts,  each  of  which  is  a  coil  of  wire,  one  being  con- 
tained wdthin  the  other,  although  they  have  no  electrical 
connection  (see  Fig.  11). 

The  inner  coil,  or  "primary,"  as  it  is  called,  consists 
of  a  few  turns  of  very  coarse  insulated  wire  wrapped 
about  a  bundle  of  soft  iron  which  is  known  as  "the  mag- 
netic core." 

The  outer  coil,  or  "secondary"  is  made  up  of  a  great 
many  turns  of  fine  insulated  wire.  It  has  been  estimated 
that  in  a  12-inch  induction  coil  the  secondary  coil  is 
wound  with  between  twenty  and  thirty  miles  of  wire. 
This,  of  course,  makes  possible  an  enormous  number  of 
"turns  of  wire"  so  that  when  we  consider  that  each  turn 
of  the  secondary  induces  a  current  in  the  turn  directly 

44 


X-RAY   MACHINES 


45 


Fig.  11. — Diagrammatic  illustration  of  the  essential  parts  of  an  induction  coil. 
A'  and  A  are  the  terminals  of  the  "primary  coil."  D  represents  the  windings  of  the 
"primary"  about  the  magnetic  core  C.  The  insulating  medium  between  the  "pri- 
mary" and  "secondary"  is  shown  at  B.  The  windings  of  the  "secondary"  coil  are 
designated  by  F,  and  the  "secondary"  terminals  by  B  and  B'. 


46  DENTAL  AND   ORAL   RADIOGRAPHY 

adjacent  to  it,  which  must  be  added  to  the  current  in- 
duced in  the  first  layer  by  the  action  of  the  primary  cur- 
rent, the  sum  total  of  the  current  coming  from  the  sec- 
ondary amounts  to  something  tremendous. 

To  compute  the  E.M.F.,  of  the  induced  current  (or 
that  coming  from  the  secondary),  we  have  but  to  remem- 
ber that  *'the  E.M.F.,  of  the  induced  current  is  to  that 
of  the  primary  current,  as  the  number  of  turns  in  the 
secondary  coil  is  to  the  number  of  turns  in  the  primary." 
For  instance,  suppose  we  have  an  induction  coil  with  10 
turns  of  wire  in  the  primary,  and  100  turns  of  wire  in 
the  secondary.  If  we  pass  a  current  of  110  volts  through 
the  ** primary,"  the  voltage  of  the  "secondary"  current 
will  be — 

110 

-^xlOO=1100  volts. 

Notwithstanding  the  great  change  in  voltage,  the  wat- 
tage of  the  secondary  current  is  the  same  as  it  was  in 
the  primary  (except  for  a  small  loss  due  to  internal  re- 
sistance). This  is  not  true,  however,  of  the  amperage. 
For  example,  if  the  primary  current  of  110  volts  carries 
5  amperes,  its  wattage  would  be  550.  The  wattage  of  the 
secondary  current  would  also  be  550,  and  since  wattage 
equals  amperes  multiplied  by  volts,  the  amperage  of  the 
secondary  current  would  be — 

550 
■jjQQ-  =  Va   ampere. 

Thus  it  will  be  seen  that  as  the  voltage,  or  E.M.F.,  is 
increased  in  the  before  described  manner,  the  amperage 
or  current  strength  is  decreased  in  equal  ratio.  It  should 
be  plain,  therefore,  that  the  original  current  running  to 
the  primary  is  not  changed  in  actual  value,  hiU  is  simply 
transformed  to  a  state  or  condition  ivliere  it  ivill  do  the 
special  work  required  of  it. 


X-RAY   MACHINES  4< 

In  our  consideration  thus  far  we  have  considered  the 
manner  in  which  an  electric  current  may  be  transformed 
from  a  low  to  the  high  voltage  necessary  to  energize  an 
x-ray  tube.  We  have  not,  however,  named  one  important 
requisite  of  a  current  to  be  used  for  this  purpose,  namely, 
that  the  current  must  flow  continuously  and  in  the  same 
direction* 

In  considering  the  manner  of  obtaining  a  current  in 
the  secondary,  we  learned  that  such  a  current  is  produced 
by  *' making"  and  ''breaking"  the  primary  current.  If 
a  continuous  current  is  to  be  kept  flowing,  we  must  utilize 
some  instrument  which  will  rapidly  ''make"  and  "break" 
the  current  in  the  primary  circuit.  Such  an  instrument 
is  known  as  an  "interrupter"  and  is  essential  to  any  in- 
duction coil. 

There  are  two  classes  of  these  instruments,  both  of 
which  utilize  some  automatic  principle,  and  are  known 
as  "mechanical"  and  "electrolytic." 

Mechanical  interrupters,  a  simple  illustration  of  which 
is  the  ordinary  vibrator  used  on  small  coils,  electric  bells, 
etc.,  will  rapidly  make  or  break  the  primary  current  and 
thereby  induce  a  fairly  constant  current  in  the  secondary ; 
but  this  form  of  interrupter  has  not  been  found  to  be  so 
satisfactory  for  x-ray  work  as  the  electrolytic  type. 

Of  the  various  forms  of  electrolytic  interrupters,  the 
Wehnelt  type  is  the  one  most  universally  used.  It  con- 
sists of  a  large  battery  jar  which  is  nearly  filled  with  a 
solution  composed  of  sulphuric  acid  one  part  and  water 
six  parts.  Into  this  solution  are  introduced  two  elec- 
trodes. The  negative  electrode  is  constructed  of  lead  and 
has  a  large  surface  exposed,  while  the  positive  electrode 
is  contained  within  a  porcelain  or  hard  rubber  tube  ex- 
tending down  into  the  solution  with  only  the  tip  or  end  of 
the  electrode  exposed.  The  tip  of  this  electrode  is  usually 
made  of  platinum.     (See  Figs.  12  and  13.) 

•The  exceptions  to  this  rule  will  be  given  later. 


48 


DENTAL  AND   ORAL   RADIOGRAPHY 


The  electrolytic  interrupter  is  connected  in  the  primary 
circuit  and  operates  briefly  as  follows:  As  the  current 
passes  from  the  platinum  point  (the  positive  electrode) 
through  the  solution  to  the  negative  electrode,  by  virtue 
of  its  chemical  action  upon  the  solution  bubbles  of  gas 
are  formed  around  the  exposed  platinum  point.  These 
bubbles  act  as  a  source  of  insulation  and  the  current 


Fig.  12. — Diagram  of  the  electrolytic  interrupter.  P,  terminal  of  the  positive 
electrode;  A'^,  terminal  of  the  negative  electrode;  T,  porcelain  sheath  or  tube  cov- 
ering the  positive  electrode;  /,  platinum  point  of  the  positive  electrode;  L,  negative 
electrode  constructed   of   lead. 

ceases  to  flow — ''It  is  interrupted."  At  the  instant  it  is 
interrupted,  the  bubbles  are  dispersed,  the  solution  again 
comes  in  contact  with  the  electrode,  and  the  current  is  re- 
established only  to  be  broken  again  and  so  on,  these 
changes  taking  place  with  tremendous  frequency.  With 
such  an  instrument  the  primary  current  may  be  inter- 
rupted from  60  to  30,000  times  a  minute.  These  inter- 
rupters are  sometimes  constructed  with  several  platinum 


X-RAY   MACHINES 


49 


to 


^ 


1 


» 

Uj 


Fig.  13. — Diagram  of  the  induction  coil.  C,  induction  coil;  P,  "the  primary;" 
S,  "the  secondary;"  E,  electrolytic  interrupter  in  circuit  with  the  primary  coil;  /,  rheo- 
stat and  inductance  control;  X,  x-ray  tube  connected  to  the  terminals  of  the  secondary 
coil. 


50 


DENTAL   AND   ORAL   RADIOGRAPHY 


points  which  makes  possible  a  greater  amperage  in  the 
current  without  decreasing  the  rate  of  interruptions.  For 
dental  radiography,  however,  a  single  point  interrupter 


Fig.    14. — Induction  coil   adapted   for  use  in  the   dental   x-ray   laboratory. 

will  usually  suffice,  and  at  most,  not  more  than  a  two 
point  interrupter  need  be  used. 

The  interrupter,  then,  serves  the  purpose  of  creating 
the  magnetic  impulses  which  keep  a  constant  current  flotu- 
ing  from  the  secondary.    We  should  bear  in  mind,  how- 


X-RAY   MACHINES  51 

ever,  that  the  current  produced  by  the  "make"  and 
"break"  are  not  currents  of  equal  strength,  the  current 
produced  at  the  "break"  having  much  the  highest  value. 
The  fact  that  this  current  is  the  strongest,  and  that  the 
magnetic  impulses  come  from  the  same  direction  (as  the 
induction  coil  is  used  on  the  direct  current)  it  prevails 
over  the  weaker.  Therefore  the  induced  or  secondary 
current  which  we  use  to  energize  the  x-ray  tube  is  the 
current  which  is  created  at  the  instant  of  the  break. 

The  other  wave,  or  that  created  by  the  "make,"  is 
current  in  the  wrong  direction,  and  is  called  "inverse 
current."  In  some  induction  coils  this  inverse  current 
is  the  source  of  much  trouble,  and  where  it  is  present 
to  any  appreciable  extent,  will  result  in  blurred  radio- 
grams. It  can  be  controlled,  however,  by  the  use  of 
"valve  tubes,"  or  a  "spark  gap,"  arranged  in  series  with 
the  x-ray  tube,  the  valve  tube  or  spark  gap  serving  the 
function  of  cutting  out  the  weaker  or  inverse  current^ 
without  interfering  to  any  appreciable  extent  with  the 
stronger  current  which  is  delivered  to  the  terminals  of 
the  x-ray  tube. 

The  induction  coil  is  used  on  the  direct  current  of  110 
or  220  volts.  Where  only  the  alternating  current  is  avail- 
able, some  means  must  be  used  to  change  the  current  from 
alternating  to  direct  before  it  enters  the  primary  circuit 
of  the  coil. 

This  change  in  the  current  can  be  accomplished  by 
the  use  of  "a  rotary  converter,"  of  which  several  makes 
are  available,  or  by  a  "chemical  rectifier."  These  recti- 
fiers generally  consist  of  two  electrodes  immersed  in  a 
solution  of  the  phosphate  salts  of  potassium,  sodium,  or 
ammonium,  one  electrode  being  made  of  aluminum,  and 
the  other  of  lead,  iron,  or  carbon.  IVhen  working  prop- 
erly, the  current  will  flow  to  the  aluminum  through  the 
solution,  but  not  away  from  it,  thus  cutting  out  one  wave 


52  DENTAL  AND   ORAL   RADIOGRAPHY 

of  the  alternating  current ;  or  it  is  possible,  by  properly- 
connecting  up  three  or  four  jars  containing  the  electrodes, 
to  utilize  both  waves  of  the  current. 

Induction  coils  are  usually  rated  as  to  power  by  the 
maximum  width  of  the  secondary  spark  gap ;  that  is,  the 
amount  of  distance  the  spark  will  jump  between  the  sec- 
ondary terminals.  For  example,  a  12-inch  induction  coil 
is  capable  of  producing  a  spark  that  will  jump  twelve 
inches  of  atmosphere.  While  these  coils  are  made  in  va- 
rious sizes,  capable  of  producing  a  spark  from  six  inches 
to  forty  inches  in  length,  there  is  no  particular  advantage 
in  using  more  than  a  12-inch  coil  for  dental  radiography. 
(See  Fig.  14.) 

Tesla,  or  High  Frequency,  Coil 

The  Tesla,  or  high  frequency,  coil  differs  considerably 
in  construction  from  the  induction  coil,  although  many 
of  its  principles  are  the  same  (Fig.  15).  In  a  way  it  is 
a  double  induction  coil  with  the  secondary  of  one  coil 
acting  as  the  primary  of  the  other  coil.  An  alternating 
current  is  utilized  in  the  primary  of  the  first  coil  and  by 
means  of  the  secondary  of  this  same  coil  is  stepped  up 
to  a  high  voltage.  This  ' '  stepped-up "  current  is  then 
carried  to  a  condenser.  As  the  current  leaves  the  con- 
denser, it  is  oscillating  at  a  great  rate  of  frequency  and 
passes  into  the  primary  of  the  Tesla,  or  second,  coil 
where  it  induces  a  current  in  the  secondary  of  this  coil. 
From  the  terminals  of  the  last  secondary,  it  is  carried  to 
the  x-ray  tube.  The  principles  involved  in  this  type  of 
apparatus  are  shown  in  Fig.  15. 

Like  the  current  of  the  induction  coil,  the  current  from 
the  Tesla  coil  is  high  in  voltage  and  low  in  amperage,  but 
unlike  the  current  from  the  induction  coil  it  is  not  uni- 
directional, but  is  alternating  in  character.  For  this  rea- 
son, it  is  considered  by  some  as  being  less  desirable  for 


X-RAY    MACHINES 


53 


-O- 


AAA 

i 


^ 


Vw\AA/WWWVV 

AA/WWWS 


Fig.  15. — Diagram  of  the  high  frequency  coil.  T,  alternating  current  transformer; 
C,  condenser;  G,  spark  gap;  R,  oscillation  transformer;  D,  high  tension  discharge  gap; 
X,  high   frequency  i-ray   tube. 


54  DENTAL  AND   ORAL   RADIOGRAPHY 

radiographic  purposes.  However,  this  apparently  ob- 
jectionable feature  is  overcome  by  using  an  x-ray  tube 
constructed  in  such  a  way  as  to  cut  out  one  wave  of  the 
current  and  thereby  produce  practically  the  same  result 
as  where  a  unidirectional  current  is  used. 

These  coils  have  the  advantage  of  being  less  cumber- 
some, require  less  space  and  are  less  expensive  than  the 
other  form  of  apparatus,  but  they  cannot  be  depended 
upon  to  do  the  character  of  work  that  the  powerful  "in- 
duction coil"  or  ''interrupterless  transformer"  will  do. 
Notwithstanding  this  fact,  this  type  of  apparatus  un- 
doubtedly has  a  place  in  the  x-ray  laboratory  of  the  den- 
tist, and  if  constructed  along  proper  lines  can  render 
splendid  service. 

Intermpterless  Transformer 

The  intermpterless  transformer  is  one  of  the  newer 
and  by  all  means  the  most  powerful  x-ray  machines  made, 
and  for  this  reason  it  is  perhaps  more  universally  used 
than  the  other  types  mentioned.  It  is  operated  by  an 
alternating  current  and  aside  from  controlling  and 
measuring  apparatus,  it  consists  of  two  principal  parts, 
a  step  up  transformer  and  a  rectifying  switch,  which 
consist  of  a  large  micinite  disc  operated  upon  a  synchron- 
ous motor. 

Where  the  direct  current  only  is  available  a  rotarj'' 
converter  is  added  to  change  the  direct  current  to  an 
alternating  current  before  it  enters  the  step-up  trans- 
former. In  the  operation  of  such  a  machine  an  alternat- 
ing current  either  from  the  source  of  current  supply  or 
from  the  rotary  converter,  as  the  case  may  be,  is  sent 
through  the  primary  of  the  step-up  transformer.  This 
induces  a  current  in  the  secondary  of  the  proper  voltage, 
but  alternating  in  character.    The  rectifying  switch  then 


X-RAY   MACHINES 


55 


changes  this  current  from  an  alternating  to  a  direct  cur- 
rent and  as  such  it  is  delivered  to  the  terminals  of  the 
tube.    Tlie  principles  involved  in  operating  either  with 
a  direct  or  alternating  current  are  shown  in  Fig.  16. 
The  interrupterless  transformer  is,  as  stated  before, 


SthCHROIiOUS  ftOTQH 


Fig.  16. — The  working  principles  of  the  interrupterless  transformer  are  here 
shown.  The  synchronous  motor  used  to  operate  the  rectifying  switch  of  the  alter- 
nating current  machine  may  also  be  used  as  a  rotary  converter  where  the  direct  cur- 
rent is  desired  for  other  purposes  in  the  laboratory. 


the  most  powerful  and  efficient  type  of  apparatus  avail- 
able for  x-ray  work.  It  is  likewise  the  most  expensive, 
which  fact  often  proves  a  stumbling  block  to  the  young 
dentist.    This  fact,  however,  should  not  be  construed  as 


56 


DENTAL   AND   ORAL   RADIOGRAPHY 


an  argument  against  it.  To  the  prospective  purchaser 
who  desires  the  very  best,  regardless  of  expense,  or  who 
expects  to  do  a  great  deal  of  radiography,  the  initial  ex- 


Fig.   17. — Interrupterless  transformer  adapted  for  use  in   the  dental  x-ray  laboratory. 


pense  should  not  be  the  prime  consideration,  as  often- 
times the  most  expensive  things  in  the  long  run  prove  a 
matter  of  economy.  In  Figs.  17  and  18,  interrupterless 
transformers  adapted  for  use  in  the  dental  x-ray  labora- 
tory are  shown. 


X-RAY   MACHINES 


57 


Step-Up  Transformer  Unit 

The  step-up  transformer  unit  is  the  newest  develop- 
ment in  the  field  of  x-ray  machines.  It  was  evolved  as 
a  result  of  the  necessity  for  compact  and  easily  operated 


Fig.    18. — Inferrupterless  transformer  adapted  for   use  in  the  dental  x-ray  laboratory. 

X-ray  apparatus  for  field  and  hospital  service  in  the  great 
war  just  passed.  While  it  is  limited  both  as  to  flexibility 
and  power  it  served  a  great  need  and  will  continue  to  be 
of  great  service  where  it  is  applicable. 


58 


DENTAL   AND   ORAL   RADIOGRAPHY 


Fig.    19. — Step-up   transformer   unit. 


Fig.  20. — Step-up  transformer  unit. 


I 


X-KAY   MACHINES 


59 


This  machine  is  operated  by  an  alternating  current 
and  consists  of  ''a  step-up  transformer"  with  Coolidge 
control  or  step-down  transformer  arranged  in  combina- 
tion with  it.    The  step-down  transformer  part  of  the  unit 


Fig.  21. — Step-up  transformer  unit. 


serves  the  purpose  of  heating  the  filament  of  a  radiator 
type  Coolidge  tube  which  is  the  only  type  of  tube  which 
operates  with  real  success  upon  these  units.  This  is  due 
to  the  fact  that  the  current  coming  from  the  step-up 
transformer  is  alternating  in  cJmracter  as  the  unit  has  no 


60 


DENTAL   AND   ORAL  RADIOGRAPHY 


rectifying  switch  to  rectify  the  current  before  it  enters 
the  tube,  therefore  the  tube  must  perform  this  function* 
In  conclusion,  I  would  emphasize  the  fact  that  the  char- 
acter of  the  radiography  which  any  physician  or  dentist 
is  able  to  do,  does  not  depend  entirely  upon  the  excellence 
of  his  laboratory  equipment.  Instances  could  easily  be 
cited  where  the  best  of  equipment  fails  to  produce  the 
highest  type  of  results,  and  vice  versa,  where  unpreten- 
tious equipment  in  some  hands  has  proved  more  than 
satisfactory.  After  all,  the  comparative  degree  of  effi- 
ciency of  the  various  types  of  x-ray  machines  must  de- 
pend largely  upon  the  judgment  and  skill  of  those  who 
operate  them. 

*The    operation    of    this    type    of    apparatus    will    be    discussed    at    more    length    in 
subsequent  chapters. 


CHAPTER  V 

REQUISITES  OF  THE  DENTAL  X-RAY 
LABORATORY 

The  requisites  of  a  dental  x-ray  laboratory  are  not 
numerous  but  consist  of — 

1st — A  so-called  x-ray  machine. 

2nd — An  x-ray  tube. 

3rd — An  adjustable  'Hube  stand"  for  holding  the  tube, 
which  should  include  a  "tube  shield"  made  of  leaded 
glass,  serving  as  a  means  of  confining  the  rays  and  as  a 
source  of  protection  to  the  operator,  and  a  lead  "com- 
pression diaphragm"  and  lead-lined  or  leaded  glass 
"compression  cylinder." 

4th — A  photographic  darkroom. 

As  x-ray  machines  have  already  been  discussed,  let  us 
now  take  up  the  others,  in  the  order  in  which  they  have 
been  given. 

X-ray  Tube 

There  are  several  varieties  of  x-ray  tubes  in  general 
use  today  and  the  student  should  become  familiar  with 
the  principles  involved  in  each  kind.  We  will  first  con- 
sider the  ordinary  "gas  tube"  which  is  the  type  which 
has  been  most  universally  used  until  recent  years.  In 
fact,  it  still  enjoys  wide  usage  and  will  probably  continue 
to  do  so  especially  where  x-ray  machines  of  the  Rhum- 
korff  and  Tesla  type  are  employed.  The  ordinary 
x-ray  tube  is  a  thin  glass  bulb  six  or  eight  inches  in 
diameter,  having  two  elongations  or  stems  projecting 
from  the  bulb  opposite  and  in  line  with  each  other  (see 

61 


62  DENTAL   AND   ORAL   RADIOGRAPHY 

Fig.  22).  One  of  these  elongations  has  within  it  a  sheet 
iron  tube  at  one  end  of  which  is  a  block  of  copper,  faced 
with  platinum  or  tungsten,  and  set  at  an  angle  of  45  de- 
grees. The  other  end  of  this  sheet  iron  tube  carries  a 
platinum  wire  which  is  sealed  into  the  glass  at  the  end  of 
the  elongation  and  connected  to  a  cap  on  the  outside 
which  serves  as  an  electrical  connection. 

The  other  elongation  carries  a  rod  at  one  end  of  which 
is  a  concave  aluminum  reflector,  the  other  end  being  con- 
nected by  means  of  a  platinum  wire  sealed  in  the  glass  to 
a  cap  on  the  outside  of  the  elongation,  and  also  serves 
as  an  electrical  connection. 

The  cancave  reflector  is  known  as  *'the  cathode"  and 
the  metallic  block  opposite  it  and  located  upon  the  end 
of  the  sheet  iron  tube  is  knowm  as  the  'target"  or 
"anode."  Above  the  anode  and  at  an  angle  there  is  an- 
other stem  projecting  which  carries  a  metallic  terminal 
known  as  the  ''assistant  anode." 

This  assistant  anode  has  a  platinum  wire  extending 
from  it  which  is  sealed  into  the  glass  and  connected  to  a 
metallic  cap  on  the  outside  of  the  tube.  The  outer  ter- 
minals of  the  assistant  anode  and  the  anode  are  connected 
by  means  of  a  spiral  spring. 

Directly  above  the  anode  on  the  top  of  the  tube  there 
is  a  small  chamber  with  an  arm  extending  from  it  at  right 
angles.  This  is  known  as  "the  regulating  chamber." 
The  arm  extension  of  this  chamber  is  filled  with  asbestos 
impregnated  with  chemicals,  and  arranged  about  or  with- 
in a  small  metal  tube  from  which  a  platinum  wire  ex- 
tends, is  sealed  into  the  glass  and  connected  to  a  metallic 
cap  on  the  outside  end  of  the  chamber  arm. 

Before  being  finally  sealed,  the  tube  is  pumped  to  a 
high  degree  of  vacuum  (about  1/100,000  part  of  an  atmos- 
phere), only  enough  air  being  left  in  it  to  afford  a  path 
for  the  passage  of  the  electric  current. 


REQUISITES   OF   DENTAL  X-RAY   LABORATORY  63 

Three  general  types  of  gas  tubes  are  made  for  radi- 
ographic work,  all  of  which  embody  the  same  general 
principles  but  var}'  according  to  the  type  of  the  machine 
upon  which  they  are  to  be  used. 

They  are  designated  as  follows : 

1.  The  coil  tube. 

2.  The  transformer  tube. 

3.  The  high  frequency  tube. 

Coil  tubes  and  transformer  tubes  are  similar  in  con- 
struction but  not  in  vacuum  (see  Fig.  23).  Coil  tubes 
are  exhausted  to  a  much  higher  degree  of  vacuum  in  or- 
der to  lessen  the  tendency  for  inverse  current,  and  give  a 
high  degree  of  penetration.  The  transformer  tube  is 
made  comparatively  low  in  vacuum  as  the  current  from 
the  interrupterless  transformer  is  entirely  free  from  in- 
verse, and  of  such  high  voltage  that  the  high  vacuum  is 
neither  necessary  nor  advisable. 

The  high  frequency  tube  differs  slightly  in  construc- 
tion from  the  coil  and  transformer  tubes  owing  to  the 
fact  that  the  high  frequency  current  is  not  unidirectional. 
Therefore,  a  means  must  be  resorted  to  for  cutting  out 
or  disposing  of  one  wave  of  the  alternating  current.  This 
is  accomplished,  as  shown  in  Fig.  24,  by  placing  the  anode 
or  target  in  the  position  occupied  in  the  coil  tube  by  the 
assistant  anode  except  that  it  extends  down  to  the  center 
of  the  tube.  Then  by  having  what  really  amounts  to  two 
cathode  terminals,  only  one  of  which  is  focused  against 
the  face  of  the  anode,  and  the  other  into  a  funnel  in  the 
back  of  the  target,  almost  the  same  effect  is  produced  as 
results  from  a  unidirectional  current. 

Connecting  the  Tube  to  the  X-ray  Machine 

In  connecting  up  the  tube  to  a  coil  or  transformer 
(Fig.  25),  the  anode  terminal  {A)  is  connected  by  means 
of  a  wire  cord  coming  from  a  reel  attached  to  the  posi- 


64 


DENTAL  AND   ORAL   RADIOGRAPHY 


tive  terminal  of  the  macliine  {A'),  and  the  cathode  ter- 
minal (C)  is  connected  in  a  similar  manner  to  the  nega- 
tive terminal  of  the  machine  (C). 

A  third  wire  cord  is  usually  run  from  a  reel  {R')  sit- 
uated on  the  machine  near  the  negative  terminal  to  the 
cap  on  the  regulating  chamber  (R).  This  third  terminal 
on  the  machine  has  a  spark  gap  between  it  and  the  nega- 
tive terminal  the  length  of  which  is  adjustable  (desig- 
nated by  S'  and  S). 

Operating  the  X-ray  Tube 

When  the  current  is  started  in  the  machine,  it  enters 
the  tube  at  the  anode*  and  passes  across  the  gap  to  the 
cathode,  from  which  it  is  reflected  back  as  the  invisible 


A — Anode. 

U- -Assistant  Anode 

C— Cathode 

D — Regulating 
Chamber 

F— Regulating     Ad- 
juster 

G — Hemisphete 

H — Connection 
Wire 

I — Assistant    Anode 
Cap 

K— Anode   Cap 

L — Cathode    Cap 

M— Cathode  Stream 

N — Focal    Point 


Fig.   22. — Diagiam   of  an  x-ray   tube. 

cathode  stream  to  strike  a  focal  point  on  the  target  where 
the  x-rays  are  produced  and  pass  out  through  the  walls 
of  the  tube  (see  Fig.  22). 

With  the  passing  of  the  current  through  the  tube,  it 
should  light  up  in  a  characteristic  manner,  forming  two 
hemispheres  which  have  a  definite  line  of  demarcation. 


•Provided  an   induction   coil   or   interrupterless   is  being  used.     If  a   Tesla   coil   is 
being    used    it    will    not    matter    as    the    current   passes    in    both    directions. 


REQUISITES    OF    DENTAL   X-RAY   LABORATORY 


65 


The  hemisphere  in  front  of  the  target  which  is  the  active 
hemisphere,  is  evidenced  by  a  green  fluorescence,  the 
shade  of  coloring  depending  npon  the  degree  of  vacuum 


Fig.  23. — The  coil   or  transformer  tube. 


of  the  tube.    The  fluorescence  of  a  highly  exhausted  tube 
will  be  a  light  yellowish  green,  a  tube  low  in  vacuum  will 


66 


DENTAL   AND    ORAL   RADIOGRAPHY 


show  a  bluish  green,  while  a  medium  tube  will  be  an  inter- 
mediate green. 

For  dental  radiography,  a  fairly  high  tube  is  indicated 


Fig.    24. — The    high    fretjuency    lube. 


and  its  vacuum  should  be  kept  as  nearly  uniform  as  pos- 
sible. This  is  made  possible  by  utilizing  the  third  ter- 
minal from  the  x-ray  machine.    By  placing  the  spark  gap 


REQUISITES    OF    DENTAL   X-RAY   LABORATORY  67 


P  & 


Fig.  25. 


«=^ 


Fig.   26. — The   hydrogen   tube. 


68  DENTAL   AND    ORAL   RADIOGRAPHY 

of  this  terminal  about  three  or  four  inches  from  the  nega- 
tive terminal  of  the  machine,  the  current  will,  when  the 
vacuum  of  the  tube  gets  high  enough  to  resist  its  pas- 
sage, pass  over  the  gap,  down  the  third  terminal  wire 
into  the  regulating  chamber  where  by  heating  the  as- 
bestos it  will  liberate  gas  and  thereby  reduce  the  vacuum 
of  the  tube. 

In  addition  to  the  general  types  of  tubes  already  de- 
scribed, there  are  certain  specialized  forms  of  tubes  which 
are  highly  useful,  and  fast  becoming  popular.  Of  these, 
the  ** hydrogen  tube"  and  the  ^'Coolidge  tube"  are,  by 
far,  the  most  important. 

Hydrogen  Tube 

The  hydrogen  tube,  shown  in  Fig.  26,  differs  from  the 
ordinary  gas  tube  in  that  in  addition  to  having  the  reduc- 
ing feature,  in  common  with  other  tubes,  it  has  the  added 
advantage  of  having  a  raising  device.  This  means  that 
the  hydrogen  tube  may  be  raised  or  lowered,  at  will.  As 
the  name  implies,  this  tube  contains  hydrogen,  which  is 
greatly  responsible  for  its  unusual  flexibility. 

It  is  claimed  for  this  tube  that  it  has  a  slightly  greater 
penetration  than  other  tubes  for  a  given  parallel  spark 
length.  The  target  is  made  of  tungsten,  and  the  cathode 
is  protected  in  the  same  manner  as  the  tubes  already 
mentioned.  Such  a  tube  must  be  operated  upon  either 
an  induction  coil  or  an  interrupterless  transformer. 

Coolidge  Tube 

The  Coolidge  tube,  shown  in  Fig.  27,  is  radically  dif- 
ferent in  design  from  the  other  tubes  already  described, 
and  is  different  in  operation,  in  that  it  is  energized  by 
two  independent  currents,  one  of  high  voltage,  and  the 
other  of  low  voltage.    For  this  reason,  certain  auxiliary 


I 


REQUISITES    OF   DENTAL   X-RAY   LABORATORY  69 

apparatus  must  be  used  with  it,  in  addition  to  the  high 
tension  current  generator.  This  auxiliary  apparatus 
consists  of  a  loiv  voltage  transformer  and  regulator,  and 
an  insulated  stand  or  shelf  for  liolding  the  transformer, 
and  am,  ammeter.  The  low  voltage  current  serves  the 
purpose  of  heating  electrically  a  spiral  filament  of  flat, 
closely  wound  tungsten  wire  located  within  a  cylinder  on 
the  cathode.  This  electrically  heated  filament  serves  the 
important  function  of  controlling  the  milliamperage  of 
the  current  passing  through  the  tube.  The  higher  the 
filament  temperature,  the  larger  the  number  of  milliam- 
peres  can  be  made  to  pass  through  the  tube  and  hence  the 
shorter  will  be  the  exposure  required. 


Fig.   27. — The  Cooliclge  x-ray  tube. 

This  tube  is  fast  becoming  popular,  due  to  the  fact  that 
it  is  rugged  of  construction,  will  stand  hard  and  continu- 
ous service,  and  because  of  its  ease  of  control,  will  give 
uniform  results.  It  is  safe  to  assert  that  its  advent 
marked  the  most  distinct  advance  in  the  field  of  roent- 
genology of  recent  years.  A  discussion  of  its  use  in  our 
work  will  be  continued  later  in  Chapter  VII. 

Tube  Stand 

The  tube  stand,  which  serves  the  purpose  of  holding 
the  tube,  should  be  sufficiently  heavy  to  support  it  against 
motion  and  vibration,  and  should  be  sufficiently  adjust- 


70 


DENTAL   AND   ORAL   RADIOGRAPHY 


Fig.  28.— The  tube  stand. 


able  so  that  the  tube  can  be  raised  or  lowered,  or  placed 
at  any  desired  angle.  Its  base  should  be  mounted  upon 
casters  so  that  it  may  be  moved  with  ease.    Such  a  tube 

The  tube  stand  niav  also  be 


stand  is  shown  in  Fig.  28. 


ItKQUISITES    OF    DENTAL   X-RAY    LABORATORY  71 


Kig.   29  W. 


I'ig.   29-C. 


72  DENTAL  AND   ORAL   RADIOGRAPHY 

attached  to  and  be  a  part  of  the  x-ray  machine  as  sho\\ai 
in  Figs.  19,  20  and  21.  This  type  of  apparatus  promises 
to  become  very  popular  as  it  makes  a  strong  appeal  to 
those  Avho  have  but  a  limited  office  space  to  give  up  to 
x-ray  apparatus. 

Tube  Shield,  Compression  Diaphragm,  and  Compression 

Cylinder 

The  tube,  tube  stand,  tube  shield,  compression  dia- 
phragm and  compression  cylinder,  when  adjusted  for 
work,  as  shown  in  Fig.  28,  really  comprise  a  single 
piece  of  apparatus.  Bearing  in  mind  the  fact  that  the 
x-raj^s  pass  out  in  every  direction  from  the  face  of  the 
anode,  or  target,  (see  Fig.  29-^)  which  is  situated  in 
the  center  of  the  tube,  it  is  necessary,  if  the  clearest  pos- 
sible shadows  are  to  be  produced,  to  use  only  those  rays 
that  have  the  same  general  direction  and  that  have  an 
equal  amount  of  penetration.  Now  it  is  known  that  the 
most  rapid  and  effective  rays  are  those  that  pass  out  at 
right  angles  from  the  cathode  stream  designated  by  PR. 
Inasmuch  as  we  desire  to  use  these  rays,  and  these  rays 
only,  in  casting  our  shadows,  we  must  establish  some 
means  of  preventing  the  other  ra^^s  {S,8,S,S)  from  es- 
caping from  the  immediate  area  surrounding  the  tube, 
and  this  is  accomplished  by  means  of  the  tube  shield, 
compression  diaphragm,  and  compression  cylinder. 

The  tube  shield  (Fig.  30),  a  sectional  diagram  of  which 
is  shown  in  Fig.  29-i^  by  TS  is  made  of  leaded  glass, 
there  being  a  sufficient  amount  of  lead  in  the  glass  to 
prevent  ordinary  rays  from  passing  through  it.  The 
compression  diaphragm  makes  up  the  floor  of  the  tube 
shield  (D),  and  is  constructed  of  sheet  lead  with  an  open- 
ing of  the  proper  size  to  allow  the  desired  rays  to  pass 
through.  The  compression  cylinder  {CC)  (Fig.  29-6')  is 
made  of  aluminum  with  a  lead  lining  or  leaded  glass 


REQUISITES   or   DENTAL   X-RAY   LABORATORY 


73 


which  serves  the  purpose  of  absorbing  any  secondary 
rays  that  have  succeeded  in  passing  through  the  dia- 
phragm. It  should  be  apparent  to  anyone  that  with 
this  apparatus,  the  only  x-rays  that  succeed  in  leav- 
ing the  immediate  area  of  the  tube  are  those  that  are 
used  to  cast  the  shadows  of  the  parts  desired,  which  is 
of  great  importance,  not  only  in  obtaining  radiograms 


Fig.    30. — Leaded   glass  tube   shield. 


that  are  sharp  and  clear  and  uniform,  but  also  to  the 
health  of  the  operator  and  others  associated  with  him  in 
the  office.* 


Arrangement  of  the  Apparatus  in  the  Office 

If  dental  x-ray  equipment  is  desired,  the  question  nat- 
urally arises,  ''Where  can  the  necessary  apparatus  be 
placed?"  While  a  separate  room  is  desirable,  it  is  by 
no  means  necessary,  as  the  ordinary  operating  room  of 
"healthy  size"  can  be  made  to  accommodate  it. 

The  x-ray  machine  and  the  tulie  stand  can  be  placed 


*The  possible  injurious  effects  of  x-ray   are   discussed   in  the   last  chapter. 


74 


DENTAL   AND   ORAL   RADIOGRAPHY 


against  the  wall  at  the  left  of  the  room,  while  any  extra 
tubes  can  be  hung  in  a  suitable  rack  upon  the  wall  Avhere 
they  will  be  out  of  harm's  way  (Fig.  31).  Arranged  in 
this  manner,  x-ray  apparatus  is  not  in  the  way,  and  is 
accessible  for  use  at  any  time. 

The  dental  chair  with  its  multitude  of  adjustments 
serves  an  important  purpose  in  the  dental  x-ray  labora- 


Fig.  31. — A  convenient  manner  of  arranging  the   necessary  apparatus  when   not   in  use. 

tory,  for  the  patient  must  be  supported  in  such  a  manner 
as  to  be  able  to  hold  perfectly  quiet  during  the  time  the 
exposures  are  made.  Omng  to  the  stability  of  the  chair 
and  its  many  adjustments,  it  will  not  only  serve  this  pur- 
pose, but  is  preferable  to  having  the  patient  lie  upon  a 
table  which  has  been  the  method  employed  by  many  radi- 
ographers in  the  past. 


REQUISITES    OF    DENTAL   X-RAY   LABORATORY 


75 


Photographic  Darkroom 

Thus  far  we  have  discussed  all  but  one  of  the  requisites 
of  the  dental  x-ray  laboratory;  viz.,  the  photographic 
darkroom.  This  is  a  very  important  requisite,  and  any- 
one attempting  to  do  radiography  without  it  is  greatly 
handicapped.  It  need  not  be  large  or  elaborate,  and  run- 
ning water  is  not  absolutely  essential,  although  it  is  an 
advantage.    A  closet  3i/2x5  feet  will  suffice  if  nothing  bet- 


Fig.    32. — The    i)ortal)le    darkiooni. 

ter  is  available.  A  broad  shelf  should  be  placed  at  one 
end  to  hold  the  developing  trays  and  other  photographic 
accessories. 

With  a  darkroom  always  available,  the  dental  radiog- 
rapher is  able  to  develop  his  plates  or  films  immediately, 
profit  by  their  findings,  or,  in  case  they  do  not  come  out 
satisfactorily,  make  others  without  subjecting  the  patient 
to  the  inconvenience  of  another  appointment. 

Whore  limited  space  precludes  the  possibility  of  a  reg- 


76  DENTAL   AND    ORAL   RADIOGRAPHY 

ular  darkroom,  a  developing  cabinet,  or  so-called  "port- 
able darkroom"  may  be  utilized.  (See  Fig.  32.)  Such 
a  cabinet  may  be  placed  upon  a  small  table  or  attached  to 
the  wall  at  the  proper  height  from  the  floor.  It  should  be 
large  enough  to  contain  the  necessary  developing  trays 
and  other  photographic  necessities.  The  front  panel 
should  be  hinged  so  as  to  permit  easy  access  to  the  in- 
terior for  the  arrangement  of  the  trays,  solutions  and 
for  their  removal  after  development.  The  ruby  lamp  for 
lighting  the  interior  should  be  an  integral  part  of  the 
cabinet  and  the  "observation  window"  at  the  top  should 
be  so  placed  that  the  operator  can  have  an  unobstructed 
view  of  the  interior.  This  window  must  be  covered  with 
ruby  glass,  and  around  it  should  be  constructed  a  shield 
which  will  shut  out  all  outside  light  while  the  operator 
is  looking  into  the  cabinet. 

With  the  portable  darkroom,  plates  and  films  may  be 
satisfactorily  developed,  but  the  process  cannot  be  car- 
ried with  the  same  degree  of  comfort  as  where  "a  reg- 
ular darkroom"  is  available.  Therefore,  any  dentist  in- 
tending to  do  any  considerable  amount  of  radiography 
can  well  afford  to  go  to  the  trouble  and  expense  of  con- 
structing a  darkroom  which  will  be  comfortable,  and  con- 
tain all  the  conveniences. 


CHAPTER  VI 
TECHNIC  OF  DENTAL  AND  ORAL  RADIOGRAPHY 

Having  discussed  the  requisites  of  the  dental  x-ray 
laboratory,  let  us  now  proceed  to  a  consideration  of  their 
application  in  the  actual  work  of  radiography. 

The  very  nature  of  the  structures  with  which  we  con- 
cern ourselves,  their  gross  as  well  as  minute  anatomy, 
renders  them  somewhat  difficult  to  radiograph,  and  neces- 
sitates a  refinement  of  technic  greater  than  that  de- 
manded for  most  of  the  other  portions  of  the  human 
anatomy.  It  would,  therefore,  seem  obvious  that  an  ac- 
curate knowledge  and  anatomic  appreciation  of  the 
structures  of  the  oral  cavity  and  associated  organs  and 
structures  is  the  first  requisite  for  successful  dental  and 
oral  radiography. 

We  should  keep  in  mind  the  fact  that  radiograms  are 
shadow  pictures,  and  that  the  effect  produced  by  the  x- 
ray  upon  the  photographic  emulsion  is  but  a  shadow- 
graphic  representation  of  the  tissues  through  which  the 
rays  have  passed.  AVe  should  also  bear  in  mind  the  fact 
that  the  x-ray  penetrates  all  matter  in  inverse  ratio  to 
its  mass  or  density  and,  therefore,  the  shadow  picture 
registered  upon  the  photographic  emulsion  is  simply  a 
record  of  the  varying  densities  of  the  tissues  through 
which  the  rays  have  penetrated. 

The  x-rays  are  particularly  applicable  to  the  dental  and 
oral  structures,  owing  to  the  fact  that  these  structures 
differ  enough  individually  in  degree  of  density  to  permit 
of  their  appearing  in  a  characteristic  manner  upon  the 
photographic  emulsion.  For  instance,  it  will  be  noted 
upon  the  examination  of  a  dental  radiogram,  that  metal- 

77 


/O  DENTAL   AND    ORAL   RADIOGRAPHY 

lie  fillings,  if  they  are  present,  appear  as  white  masses, 
and  root  fillings  as  somewhat  less  dense  lines.  The 
enamel  and  dentin  are  next  in  density,  and  root  canals 
shoAv  plainly  as  dark  channels  in  the  dentin,  while  the 
alveolar  process  and  maxillte  show  their  fine  uniform 
cancellous  structure  in  various  degrees  of  density  de- 
pending upon  their  thickness. 

As  a  tooth  is  much  more  dense  than  the  bony  structures 
of  the  jaw,  any  anomaly  of  form,  size  or  position  in  the 
jaws  is  easily  discernible  even  though  it  occupy  a  posi- 
tion far  from  what  might  be  expected;  as  for  instance, 
impacted  molars,  teeth  in  the  antrum,  etc. 

Due  to  the  fact  that  the  structures  within  the  field  of 
our  specialty  have  a  characteristic  appearance  under  nor- 
mal conditions,  any  alterations  or  change  in  these  struc- 
tures is  at  once  evident  upon  the  plate.  We  thus  are 
afforded  a  means  of  studying  ititra  vitam  the  gross  pa- 
thology of  the  structures  of  the  oral  cavity. 

I  would  again  emphasize  a  point  previously  made ;  viz., 
that  a  radiogram  is  not  a  photograph,  but  a  shadow  pic- 
ture which  is  produced  by  using  the  x-ray  as  the  source 
of  illumination  and  the  photographic  plate  or  film  as  a 
screen  for  recording  permanently  the  shadows  cast. 

Therefore,  in  making  radiograms,  we  must  adhere  to 
the  same  rules  which  apply  in  making  correct  shadoAvs 
with  ordinary  light.  If  correct  shadows  are  cast,  a  cer- 
tain definite  relationship  must  exist  between  the  source 
of  illumination,  the  object,  and  the  screen.  Any  change 
or  variance  in  this  relationship  will  result  in  a  changed 
image.  A  simple  experiment  will  suffice  to  illustrate  to 
a  beginner  the  truth  of  this  statement. 

Use  a  piece  of  ordinary  white  writing  paper  as  a  screen 
and  hold  it  about  two  feet  away  from  a  lamp,  and  place 
your  hand  or  any  other  small  object,  midway  between  the 
lamp  and  the  improvised  screen,  and  observe  the  shadoAv 


DENTAL,   AND    ORAL   RADIOGRAPHY   TECHNIC  iV 

east.  You  will  note,  first,  that  it  is  very  much  enlarged ; 
and,  second,  that  it  is  very  faint  and  indistinct.  Now, 
slowly  move  the  object  toward  the  screen.  As  it  ap- 
proaches, the  shadow  becomes  more  distinct  and  smaller 
until  at  length  when  the  object  is  almost  touching  the 
screen,  the  shadow  will  be  good,  black  and  distinct,  and 
of  practically  the  exact  size  of  the  actual  object.  It  will 
also  be  found  that  the  shadow  can  be  altered  by  chang- 
ing the  position  of  the  light,  that  is,  moving  it  toward  the 
object  or  away  from  it,  by  lowering  it  below  the  level  of 
the  object  or  raising  it  higher  than  the  object ;  or  by  mov- 
ing it  to  the  right  or  to  the  left.  Eventually,  however, 
a  point  can  be  found  which  will  cause  the  shadow  to  as- 
sume its  most  correct  proportions  as  well  as  its  sharp- 
est outline.  When  this  point  is  established,  the  light  rays 
will  be  traveling  in  a  perpendicular  direction  to  a  plane 
which  lies  midway  between  the  plane  of  the  object  and 
the  plane  of  the  screen,  and  the  light  will  be  placed  at 
what  we  call  the  proper  focal  distance. 

Applying  the  laws  deduced  from  this  simple  illustra- 
tion of  shadow  making  to  radiography,  we  learn,  first, 
that  the  closer  we  can  l)ring  the  photographic  plate  or 
film  to  the  tissues  we  wish  to  show,  the  clearer  and 
sharper  will  be  the  resulting  radiogram;  second,  that  the 
x-rays  in  passing  through  the  tissues,  must  travel  per- 
pendicularly to  a  line  which  lies  midway  betw^een  the 
plane  of  the  tissues  desired  and  the  plane  occupied  by 
the  photographic  plate;  and  third,  that  the  source  of  the 
x-ray  production  (the  target  of  the  tube)  nuist  be  placed 
at  a  proper  focal  distance. 

In  order,  therefore,  to  obtain  a  radiogram  of  any  por- 
tion of  the  body,  it  is  necessary  to  have  a  photographic 
or  x-ray  plate,  or  film  (properly  prepared  so  as  to  ex- 
clude all  light  and  moisture),  placed  in  such  a  position 
that  the  rays  passing  through  the  structures  desired,  will 


80  DENTAL   AND   ORAL   RADIOGRAPHY 

register  their  shadows  Avith  the  least  amount  of  distor- 
tion possible  upon  the  plate  or  film. 

In  securing  radiograms  of  the  dental  and  oral  stnic- 
tures,  two  general  methods  of  procedure  are  open  to  us, 
each  of  which  has  its  values  and  special  indications. 
These  are  known  as  the  "intra-oral"  and  "extra-oral" 
methods. 

With  the  first,  only  small  films  are  used  which  are 
placed  within  the  month  opposite  the  area  to  be  radio- 
graphed, and  held  in  position  either  by  means  of  a  tray 
or  film  holder,  or  by  the  assistant,  or  better  still,  by  the 
patient  exerting  slight  pressure  with  the  finger.  This 
method  is  indicated  where  radiograms  of  small  areas  only 
are  desired,  as,  for  instance,  two  or  three  of  the  teeth, 
with  the  adjacent  alveolar  process. 

With  the  other  method  of  procedure  mentioned;  viz., 
the  "extra-oral"  method,  large  plates  or  films  are  used 
and  the  areas  desired  are  brought  in  as  close  contact  as 
possible  with  the  plate  by  pressing  or  resting  the  face 
against  it.  The  x-rays  are  then  passed  through  the  struc- 
tures from  the  other  side  of  the  skull,  and  oftentimes 
must  pass  through  the  entire  face  or  skull,  in  transit. 

When  using  this  method,  large  areas  may  be  radio- 
graphed, which  in  some  instances  will  embrace  the  lateral 
halves  of  both  the  upper  and  lower  jaws  from  the  cuspid 
region  anteriorly  to  the  angle  of  the  jaiv  posteriorly,  and 
from  the  floor  of  the  orbit  above  to  the  inferior  margin 
of  the  mandible  below.  In  fact,  it  is  possible  by  making 
several  exposures  to  obtain  in  detail  a  shadowgraphic 
representation  of  the  dental  apparatus  in  toto,  as  well 
as  its  associated  organs  and  structures,  the  nasal  cavity 
and  pneumatic  sinuses,  the  maxilla  and  the  mandible. 

It  should  be  apparent  to  anyone  that  the  first  method 
greatly  reduces  the  possibilities  of  the  x-ray.  Both  metJi- 


DENTAL    A2^^D    ORAL   RADIOGRAPHY    TECHNIC  81 

ods  have  their  advantages  and  neither  should  he  dis- 
carded in  favor  of  the  other. 

Intra-oral  Method 

We  shall  first  discuss  the  intra-oral  method  by  which 
small  areas  are  radiographed.  First  of  all,  the  patient 
should  be  placed  in  a  comfortable  position,  and  the  head 
supported  so  that  it  may  he  held  perfectly  still.  After 
the  tube  and  workino^  current  has  been  tested  out  and 


Fig.  33. — The  patient  can  hold  the  film  in  position  against  the  upper  teeth  by  exerting 
slight   pressure    with   the   thumb. 

the  proper  degree  of  vacuum  established,  the  tube  stand 
(complete  with  the  other  apparatus  before  described)  is 
moved  to  a  position  where  the  rays  coming  from  the 
tube,  through  the  compression  diaphragm  and  cylinder 
can  be  made  to  pass  through  the  desired  areas  and  cast 
their  shadows  upon  the  small  film  within  the  mouth 
(Fig.  33). 
In  using  this  method  upon  the  upper  teeth,  tlie  great- 


82 


DENTAL   AND   ORAL   RADIOGRAPHY 


est  care  must  be  exercised  if  the  shadows  produced  are 
free  from  distortion,  for  the  film  must  be  held  within  the 
upper  arch  against  the  lingual  side  of  the  teeth  and  the 
palate,  and  must  occupy  a  position  Avhich  is  in  a  different 


rig.    34. — Correct   ami    incorrect    techiiic. 


plane  from  that  occupied  by  the  roots  of  the  teeth.  When- 
ever it  is  necessary  to  direct  the  rays  upon  structures  tliat 
lie  at  an  angle  with  the  plate  or  film,  correct  shadows 
may  be  obtained  by  adhering  to  the  following  rule :    ''Bi- 


I 


DENTAL   AND    ORAL   RADIOGRAPHY   TECHNIC  8d 

sect  the  angle  made  hy  the  plane  of  the  object,  and  the 
plane  of  the  film,  and  direct  the  rays  so  that  they  ivill 
fall  perpendicular  to  this  bisected  plane.' ^ 

Failure  to  adhere  strictly  to  this  rule  is  one  of  the 
most  common  causes  of  partial  or  complete  failure  in 
producing  true  shadowgraphic  representations  of  the 
dental  structures.  For  instance,  if  the  rays  are  directed 
from  too  loiu  a  source,  the  shadoivs  ivill  be  lengthened, 
or  if  they  be  directed  from  too  high  a  source,  the  shad- 
oivs ivill  be  foreshortened,  the  amount  of  elongation  or 
foreshortening  being  in  direct  proportion  to  the  amount 
of  deviation  from  the  proper  focal  point. 

The  importance  of  adhering  strictly  to  this  rule  is 
graphically  shown  in  Fig.  34,*  where  an  upper  central 
incisor  and  the  adjacent  teeth  are  radiographed.  In  the 
upper  picture  (A)  the  rays  are  passing  in  from  too  low 
a  source  with  the  result  that  the  image  imposed  upon  the 
film  is  lengthened  to  the  extent  that  the  resulting  radio- 
gram is  useless.  In  the  center  picture  (B)  the  rays  are 
coming  from  too  high  a  source,  the  result  being  a  short- 
ened image.  Such  a  radiogram  has  but  little  value  and 
in  many  instances  would  prove  very  misleading.  In  the 
lower  picture  (C)  the  rays  are  passing  in  at  the  cor- 
rect angle;  viz.,  they  are  directed  perpendicularly  to  a 
plane  which  lies  midway  between  the  plane  of  the  teeth 
desired  and  the  plane  of  the  film.  The  result  is  a  radio- 
gram in  which  the  images  of  the  teeth  desired  are  im- 
posed upon  the  film  in  their  correct  proportions. 

It  will  be  noted  upon  a  close  examination  of  this  last 
radiogram  (C)  that  an  alveolar  abscess  is  present  at  the 
apex  of  the  root  of  the  right  central  incisor.  By  examin- 
ing the  other  radiograms  {A  and  B)  it  will  be  seen  that 
this  condition  is  not  apparent  in  them,  which  lends  em- 
phasis to  the  importance  of  an  exact  technic. 


Technic   of   Dr.    Weston   Price. 


84 


DENTAL  AND   ORAL   RADIOGRAPHY 


The  teclmic  illustrated  (by  C  of  Fig.  34)  is  indicated 
for  all  of  the  upper  teeth.  Occasions  may  arise,  however, 
where  it  will  not  suffice  for  the  upper  molar  teeth  owing 


Fig.    35. — Technic   for    the   upper   molar   teeth. 

to  the  fact  that  the  buccal  roots  and  the  lingual  roots  may 
diverge  to  the  extent  of  assuming  different  planes.  In 
this  event,  it  may  be  necessary  to  make  more  than  one 


DENTAL    AND    ORAL   RADIOGRAPHY    TECHNIC  85 

radiogram,  if  information  of  an  exacting  character  is  de- 
sired concerning  an  upper  molar.  The  plan  of  procedure 
is  shown  in  Fig.  35,  A,  B,  and  C. 

If  a  general  picture  of  the  molar  is  desired  (shown  by 
A),  the  plane  of  the  tooth  is  assumed  as  lying  midway 
between  buccal  roots  and  lingual  root,  and  the  rays  are 
passed  in  perpendicularly  to  the  plane  lying  midway  be- 
tween this  assumed  plane  ^nd  the  film.  In  the  resulting 
radiogram  none  of  the  roots  will  appear  in  their  exact 
proportions,  but  the  buccal  roots  will  be  slightly  short- 
ened, while  the  lingual  root  will  be  slightly  lengthened. 


\ 


w 


#^- 


.  -J 

Fig.    36. — Special   compression   cylinder   made    of   leaded   glass. 

When  it  is  desirable  to  obtain  a  radiogram  of  the  buc- 
cal roots  in  their  exact  length,  they  must  be  assumed  as 
being  the  plane  of  the  tooth  (B)  and  the  rays  must  pass 
in  perpendicularly  to  a  plane  lying  midway  between  them 
and  the  film.  In  this  event,  the  image  of  the  lingual  root 
is  elongated. 

If  the  lingual  roots  are  under  scrutiny  (C),  they  must 
be  considered  the  plane  of  the  teeth,  and  the  rays  passed 
in  perpendicularly  to  a  plane  lying  midway  between  the 
lingual  root  and  the  film.  In  this  event,  the  image  of 
the  lingual  root  ivill  have  its  correct  proportions,  but  the 
image  of  the  buccal  roots  will  be  slightly  shortened. 


86 


DENTAL   AND   ORAL   RADIOGRAPHY 


The  upper  molars  are  by  all  means  the  most  difficult 
teeth  to  radiograph;  that  is,  to  obtain  radiograms  that 
are  as  comprehensive  as  those  made  of  the  other  teeth. 
However,  by  going  to  the  extra  work  entailed  by  the 
foregoing  procedure,  valuable  radiographic  information 
can  oftentimes  be  gained. 

The  task  of  radiographing  the  upper  molars  and  pre- 
molars can  be  rendered  less  difficult  by  using  a  special 
compression  cylinder  made  of  leaded  glass,  as  sho\\Ti  in 


Fig.   37. — The  patient   can   hold   the   film   in   position   against   the   lower   teeth   by   exert- 
ing  slight   pressure  with   the   finger. 

Fig.  36.*  The  end  of  the  glass  cone  or  cylinder  is  beveled 
at  the  end  so  that  it  can  be  placed  close  to  the  face  and 
still  remain  at  the  desired  angle,  its  glass  construction 
enabling  the  operator  to  view  the  area  under  exposure 
at  all  times,  and  thereby  lessen  the  liability  of  inaccurate 
work. 

Witli  tlie  lower  teeth  (Fig.  37)  we  do  not  have  this  diffi- 
culty to  contend  with  to  so  great  a  degree,  as  the  films 
can  be  placed  for  the  most  part  in  such  a  position  that 

•Suggested  by  Dr.  F.  K.  Ream. 


DENTAL   AND    ORAL   RADIOGRAPHY   TECHNIC  87 

they  lie  parallel  to  the  long  axis  of  the  teeth,  and  the  rays 
can  be  directed  in  a  perpendicular  direction  both  to  the 
plane  of  the  teeth  and  the  plane  of  the  film. 

In  placing  the  films  in  the  mouth  preparatory  to  mak- 
ing radiograms  of  the  lower  teeth,  difficulty  is  sometimes 
encountered,  owing  to  the  fact  that  the  tissues  are  usually 
quite  sensitive.  Inasmuch  as  the  film  must  be  pressed 
well  down  hetiveen  the  tongue  and  the  teeth,  it  is  advis- 
able to  first  see  that  no  sharp  corners  exist  on  the  film 
covering,  or  better  still,  provide  a  rubber  envelope  or 
film  holder  ivhich  has  no  sharp  corners.  Such  an  en- 
velope is  easily  improvised  by  the  use  of  ordinary  black 
vulcanite  rubber.  A  piece  of  this  rubber  which  sliould  be 
a  little  more  than  double  the  size  of  the  film,  is  wrapped 
about  it  and  the  free  edges  pressed  together.  These  edges 
are  then  trimmed  with  a  pair  of  scissors  so  that  the  cor- 
ners are  rounded.  Such  an  envelope  containing  the  film 
can  be  introduced  into  the  mouth  and  placed  well  down 
on  the  lingual  side  of  the  teeth  with  a  minimum  amount 
of  discomfort  to  the  patient.  Realizing  the  discomfort  to 
patients  arising  from  the  film  comers,  manufacturers  are 
now  making  films  with  soft  metal  backs  with  the  corners 
rounded.  Such  films  are  decidedly  preferable  for  the 
lower  teeth. 

Film  Holders. — Some  operators  prefer  to  use  a  film 
holder  to  support  the  film  during  exposure.  Of  these, 
there  are  several  varieties  upon  the  market,  all  of  which 
will  accomplish  the  work  for  which  they  are  intended. 

The  Leach  Film  Holder  (Designed  by  Dr.  F.  D. 
Leach). — The  Leach  film  holder  is  very  simple  in  design, 
and  two  film  holders  constitute  a  set.     (See  Fig.  38.) 

With  these,  the  patient  holds  the  film  in  position  by 
grasping  the  handle  part  of  the  holder,  and  the  operator 
can  by  noting  the  angle  of  the  handle,  determine  the  di- 
rection in  which  the  rays  must  be  directed. 


88 


DENTAL   AND   ORAL   RADIOGRAPHY 


The  smaller  holder  is  designed  for  the  upper  six  and 
lower  eight  anterior  teeth,  and  the  larger  holder  is  de- 
signed for  the  posterior  areas  of  the  mouth. 

The  Dorr  Film  Holder  (Designed  by  Dr.  P.  P.  Dorr). 
— The  Dorr  film  holder  is  designed  so  that  the  film  is 
held  in  position  for  exposure  by  closing  the  teeth  upon 
a  flange  which  is  part  of  the  holder.  (See  Fig.  39.)  A 
removable  handle  is  attached  to  the  edge  of  the  flange 
and  assists  in  placing  the  film  holder  (carrying  the  film) 


0=n 


Fig.    38. — The   I<each   film   holder. 

in  the  desired  position  in  the  mouth,  after  which  the 
handle  can  be  removed. 

Two  film  holders  constitute  a  set  of  which  one  has  an 
obtuse  angle  and  is  designed  for  the  upper  teeth,  while 
the  other  is  placed  at  right  angles  to  the  flange  and  is 
intended  for  use  upon  the  lower  teeth. 

AVhere  it  is  necessary  to  make  a  complete  radiographic 
examination  of  the  dental  arches,  it  can  be  accomplished 
in  the  average  case,  by  making  six  exposures  of  each 
arch.    The  procedure  to  be  followed  is  diagrammatically 


DENTAL   AND   ORAL   RADIOGRAPHY   TECHNIC 


89 


shown  in  Fig.  40.  The  numbers  1,  2,  3,  4,  5,  6  indicate  the 
position  of  the  x-ray  tube  in  its  relation  to  the  dental 
arch,  and  the  ends  of  the  lines  coming  from  the  numbers 
show  the  position  of  the  mesial  and  distal  edges  of  the 
film  used  for  each  exposure.  It  will  be  noted  that  each 
adjacent  film  position  overlaps  its  neighbor  which  is  ad- 
visable so  that  no  area  is  left  out. 


Fig.    39. — The   Dorr   film   holder   with   detachable    handle. 


Fig.    40. 

In  making  radiograms  of  the  anterior  part  of  the  arch, 
it  is  a  mistake  to  attempt  to  radiograph  more  than  two 
or  three  teeth  at  a  time,  as  the  curvature  of  the  arch 
usually  renders  it  impossible  to  get  more  than  that  num- 
ber free  from  distortion. 

Another  point  in  technic  which  should  not  be  over- 


90 


DENTAL   AND   ORAL   RADIOGRAPHY 


looked  if  sharp  outlines  are  to  be  obtained,  is  the  one  in 
regard  to  having  the  tube  placed  at  the  proper  distance 
from  the  structures  to  be  radiographed.  To  establish  the 
best  focal  distance  for  Avork  about  the  teeth  or  jaws,  the 
target  of  the  tube  should  be  about  twenty  inches  from  the 
plate  or  film. 

Another  method  of  holding  a  film  in  position  for  ex- 
posure which  has  not  been  alluded  to  so  far  is  known  as 


Fig.    41-^. --Method   of   obtaining   a   radiogram    of   the   upper   incisor    region    using   the 

bite    method. 


the  "bite  method,"  and  while  it  is  limited  in  its  useful- 
ness can  sometimes  be  employed  to  advantage.  It  con- 
sists of  placing  a  large  film  about  ly^  x  2i/4  in  size  in  the 
mouth  and  having  the  patient  close  the  teeth  against  it 
and  thereby  hold  it  in  place  during  the  exx^osure. 

Owing  to  the  fact  that  a  film  held  in  this  manner  is 
not  brought  in  close  contact  with  the  teeth  except  at 
their  occlusal  surfaces  the  images  of  the  apical  portions 


I 


DENTAL   AND   ORAL   RADIOGRAPHY    TECHNIC 


91 


cannot  be  shown  as  clearly  as  they  should  be  if  the  high- 
est possible  degree  of  detail  is  desired.  Furthermore, 
the  x-rays  must  be  passed  in  through  the  tissues  at  a 
much  more  decided  angle  than  is  necessary  where  the 
standard  technic  is  used. 

However,  occasions  may  arise  where  this  plan  will 
prove  advantageous  especially  where  deeply  imbedded 
or  impacted  teeth  in  the  mandible  lie  out  of  reach  of  the 


I'ig.    41 -B. — Method   of   obtaining   a    radiogram    of   the    lower    incisor   region    using    the 

bite    method. 

ordinary  small  films  placed  between  the  tongue  and  the 
teeth.  The  technic  employed  in  such  cases  is  shown  in 
Figure  41-B. 

The  time  factor  will  not  be  discussed  at  this  juncture 
except  to  say  that  with  a  good  x-ray  machine,  and  a 
properly  regulated  tube,  good  radiograms  can  be  ob- 
tained by  very  short  exposures  in  using  the  intraoral 
method,  as  the  rays  need  only  penetrate  a  comparatively 


92 


DENTAL   AND   ORAL   RADIOGRAPHY 


short  distance  before  reaching  the  fihns.  In  fact,  witli 
the  apparatus  now  available,  radiograms  can  often  be 
obtained  by  instantaneous  exposures.  However,  instan- 
taneous exposures  are  not  necessary  for  good  radiog- 
raphy. X-ray  apparatus  which  is  capable  of  producing 
sharp,  clear  "intra-oral"  radiograms  in  from  two  to 
five  seconds,  is  efficient  enough  for  use  in  the  x-ray  lab- 
oratorv  of  the  dentist. 


I 


CHAPTER  VII 

TECHNIC  OF  DENTAL  AND  ORAL  RADIOGRAPHY 

(Continned) 

Extra-oral  Method 

The  extra-oral  method  is,  in  the  author's  opinion,  one 
which  offers  a  very  \mle  range  of  nsefuhiess  in  our  work. 
As  stated  previously,  this  is  the  method  used  to  obtain 
radiograms  of  large  areas.    Not  only  can  larger  areas  be 


Fig.   42. — The  headrest   of  the  dental  chair  with   its  many   adjustments   can   easily  be 
arranged  so  that  the  patient's  head  may  rest  easily  and  firmly  upon  it. 

obtained  by  this  method,  but  locations  and  structures  in- 
accessible to  the  small  films  are  reached  and  their  images 
accurately  and  clearly  recorded  upon  the  larger  plates. 
Therefore,  the  advantages  of  becoming  familiar  with  this 
method  are  well  worth  while. 

93 


94 


DENTAL   AND   ORAL   RADIOGRAPHY 


I 


Fig.    A3-A. — Tube   stand    with   platerest   and   head   support.      (Eisen   and    Ivy.) 


Fig.   43-5. — Position   of   head   and   angle   for  left  side   of  jaws.      (I'Cisen   and   Ivy). 


DENTAL   AND   ORAL  RADIOGRAPHY   TECHNIC  95 

The  technic  is  simple  when  once  mastered,  but  must  be 
adhered  to  accurately  if  the  results  are  to  be  depended 
upon  for  diagnosis.  In  using  the  extra-oral  method,  large 
plates  or  films  are  used  and  the  areas  desired  are  brought 
in  as  close  contact  as  possible  with  the  plate,  hy  pressing 
or  resting  the  side  or  portion  of  the  face  upon  ivhich 
the  structures  desired  are  located,  against  the  plate. 

First  of  all,  the  patient  must  be  placed  in  a  position  so 
that  the  head  can  he  held  perfectly  still.  The  dental  chair 
with  a  few  adjustments  offers  an  excellent  means  for 
accomplishing  this  and  may  be  used  in  any  one  of  several 
ways.  For  instance,  one  of  the  chair  arms  can  be  lowered 
down  against  the  side  of  the  chair  or  removed,  and  the 
patient  placed  sideways  in  the  chair.  The  chair  back  is 
then  adjusted  so  that  the  patient  lies  against  it  in  an  easy 
position,  and  the  headrest  wings  are  adjusted  so  as  to 
lie  fiat  and  thereby  form  an  excellent  resting  place  for  the 
plate.  The  headrest  with  its  many  possible  adjustments 
can  easily  be  placed  so  that  the  patient's  head  rests  easily 
and  firmly  upon  the  plate,  rendering  it  an  easy  matter  to 
remain  perfectly  quiet.  This  position  is  shown  in  Fig. 
42. 

For  this  character  of  work  some  operators  prefer  to 
use  a  platerest  and  head  supporting  device  attached  to 
the  tube  stand  as  shown  in  Fig.  43-^.  Where  such  a 
method  is  followed,  the  head  is  supported  in  its  proper 
relationship  to  the  plate  as  shown  in  Fig.  43-^.* 

Author's  Methods  of  Seating  the  Patient 

In  the  author's  opinion,  there  is  another  method  of 
seating  the  patient  for  this  character  of  work  which 
will  be  found  to  1)(;  advantageous  where  such  special  ap- 
paratus is  not  available.    It  is  accomplished  by  using  an 

•Kisen,  IC.  J.,  and  Ivy.  Robert  IT.:    American  Journal  of  Roentgenology,  May,  1916. 


96     .  DENTAL  AND   ORAL  RADIOGRAPHY 

ordinary  chair  with  a  straight  back  and  small  arms, 
placed  against  the  back  of  the  dental  chair.  The  head- 
rest of  the  cliair  is  turned  over  and  adjusted  to  the 
proper  height,  position  and  angle,  so  that  the  patient's 
head  can  rest  against  it  in  any  desired  position.  In  this 
way  the  patient  is  afforded  the  firm  support  of  the  heavy 


Fig.   44. — The  arrangement   of  the  apparatus  preparatory  to  seating  the  patient. 

dental  chair,  and,  therefore,  has  little  difficulty  in  re- 
maining perfectly  quiet,  and  the  operator  can  by  making 
a  few  changes  in  the  position  of  the  small  chair,  by  mov- 
ing and  readjusting  the  tube  stand  and  the  headrest, 
have  radiographic  access  to  any  part  of  the  oral  cavity 
or  associated  structures.    The  arrangement  of  the  appa- 


DENTAL   AND    ORAL   RADIOGRAPHY   TECHNIC 


97 


ratiis  preparatory  to  seating  the  patient  is   shown  in 
Fig.  44. 

The  fact  that  this  requires  but  a  few  moments,  does 
not  materially  disarrange  the  office,  or  put  the  patient  to 
discomfort,  justifies  the  author  in  feeling  that  it  is  an 


Fig.  45. — The  patient  seated  and  the  apparatus  arranged  for  making  a  radiogram 
of  the  left  side.  The  comfortable  position  of  the  patient  renders  it  an  easy  matter 
to  remain  perfectly  quiet. 


excellent  method  for  use  in  the  average  dental  office. 
(Fig.  45.) 

In  order  to  expedite  the  making  of  radiograms  of  this 
character  the  author  has  designed  a  special  "plate  and 


head  rest  table"  which  is  shown  in  Fig.  46. 


In  using 


98 


DENTAL    AND    ORAL    RADIOGRAPHY 


Fig.    46. — Plate   and   head-rest   support   for   extra-oral    radiography. 


Fig.   47. — .plate  and  head-rest   support  adjusted   to   the   arras   of  the   dental   chair. 


DENTAL   AND    ORAL   RADIOGRAPHY    TECHNIC  99 

this  apparatus  the  patient  is  seated  in  an  ordinary  office 
chair  and  the  table  is  then  moved  close  up  to  the  patient 
so  that  the  elbows  and  forearms  rest  upon  the  table  and 
the  face  is  allowed  to  rest  upon  the  head  and  plate  sup- 
port, which  is  adjustable  in  height.  The  apparatus  can 
be  so  arranged  that  the  patient  rests  in  an  easy  com- 
fortable position  and  therefore  can  remain  perfectly 
quiet  as  long  as  necessary.  When  not  in  use  the  table 
is  placed  against  the  wall  where  it  is  out  of  the  way. 

After  satisfactorily  using  this  method  of  supporting 
the  head  for  some  time,  the  author  modified  this  table 
so  that  it  could  be  adjusted  to  the  arms  of  the  dental 
chair  as  shown  in  Fig.  47.  This  is  proving  a  distinct 
advantage  as  it  requires  but  a  moment's  time  to  place 
the  table  in  position  and  renders  it  unnecessary  to  re- 
move the  patient  from  the  chair  regardless  of  the  char- 
acter of  radiography  which  is  to  be  attempted. 

With  the  head  thus  supported,  as  shown  in  Figs.  45  or 
46,  the  rays  are  directed  from  the  opposite  side  of  the 
head,  and,  therefore,  must  pass  through  the  entire  face 
or  skull  in  transit.  The  question  naturally  arises,  how  is 
this  to  be  accomplished  without  superimposing  the  shad- 
ows of  one  side  upon  the  shadows  of  the  other  side,  and 
thereby  producing  a  chaotic  result. 

For  instance,  let  us  suppose  that  we  wish  to  obtain 
a  radiogram  of  the  left  side  of  the  upper  and  lower  jaws 
extending  from  the  cuspid  region  in  front  to  the  angle 
of  the  jaw  behind,  and  from  the  floor  of  the  orbit  above 
to  the  inferior  margin  of  the  mandible  below.  If  we  are 
to  get  a  correct  shadowgraphic  representation  of  this 
area,  it  should  be  free  from  the  shadows  of  the  opposite 
side,  and  this  can  only  be  accomplished  hy  directing  the 
rays  in  such  a  manner  that  they  ivill  miss  the  areas  not 
desired  and  will  pass  through  those  we  wish  to  record. 

In  accomplishing  this,  we  must  take  into  consideration 


100 


DENTAL   AND   ORAL   RADIOGRAPHY 


Fig.   48-^. 


Fig.   48 -B. 

Fig.  48-B.^Technic  for  left  side.    M-L,  median  line;  S,  the  spine;  A,  ascending  ramus 
and  angle  of  lower  jaw;  P-F,  plate  or  film. 


DENTAL    AND    ORAL   RADIOGRAPHY   TECHNIC  101 


Fig.   49-A. 


Fig.  49-S. 

Fig.   49B. — Techiiic   for   right   side.     M-L,   median   line;    S,   the   spine;    A,    ascending 
ramus  and  angle  of  lower  jaw;  P-P,  plate  or  film. 


102 


DENTAL   AND   ORAL   RADIOGRAPHY 


two  structures ;  viz.,  the  spine  and  the  ascending  ramus 
of  the  mandible  (on  the  right  side  in  this  instance  as 
the  left  side  is  to  be  radiographed)  and  cause  the  rays 
to  pass  in  through  this  opening  and  thereby  reach  the 


Fig.    SO. 

desired  area.    The  way  in  which  this  is  accomplished  is 
shown  in  Fig.  48,  A  and  B,  and  Fig.  49,  A  and  B. 

An  important  factor  in  accomplishing  this  is  the  posi- 
tion in  which  the  patient's  head  is  held  as  it  is  pressed 
against  the  plate.    Held  in  the  manner  shown,  the  rays 


DENTAL    AND    ORAL    RADIOGRAPHY    TECHNIC 


103 


Fig.  51-A. 


Fig.    Sl-B. — Incorrect    tcchnic. 


Fig.    51-J3. 

The    shadows    of    both    sides    will    be    imposed    upon 
the  plate. 


104  DENTAL   AND   ORAL   RADIOGRAPHY 

can  be  made  to  pass  in  between  the  ascending  ramus  of 
the  mandible  and  the  spine,  and  can  pass  in  at  approxi- 
mately a  perpendicular  direction  to  the  long  axis  of  the 
teeth  and  the  plate,  giving  correct  shadow  lengths  upon 


Fig.  52. — The  result  of  incorrect  technic.     This  is  a  radiogram  of  the  same  subject  as 

shown   in    Fig.    SO. 

the  plate.    Fig.  50  shows  a  radiogram  made  by  using  this 
technic. 

If  this  rule  is  disregarded  and  the  rays  passed  through 
the  structures,  as  shown  in  Fig.  51,  A  and  B,  the  shadows 


DENTAL   AND   ORAL  RADIOGRAPHY   TECHNIC 


105 


Fig.   53-A. 


Fig.    53B. 

Fig.  53. — The  areas  in  the  upper  and  lower  jaws  extending  from  the  median  line 
to  the  first  premolar  can  be  radiographed  by  utilizing  this  technic.  A,  technic  for 
left  side;   B,  technic  for  right  side. 


106 


DENTAL  AND   ORAL  RADIOGRAPHY 


of  the  opposite  side  will  be  superimposed  upon  the  shad- 
ows of  the  structures  desired,  and  a  chaotic  result  pro- 
duced. The  result  of  such  technic  is  shown  in  Fig.  52. 
In  a  similar  manner  as  shown  in  Figs.  48  and  49,  with 
slight  adjustments  in  the  position  of  the  plate,  the  head, 
and  the  tube,  the  areas  in  the  upper  and  lower  jaws  ex- 
tending from  the  median  line  to  the  first  premolars,  and 
from  the  nose  above  to  the  inferior  margin  of  the  man- 
dible below,  can  be  radiographed  (Fig.  53,  A  and  B). 
Lil^ewise  the  structures  at  the  median  line  including  the 


A— 


Fig.    54. — The   structures   at    the   median   line   including  the   incisors,    both   above    and 
below,  may  be  secured  in  this  way. 

incisors,  both  above  and  below,  the  anterior  portions  of 
the  mandible  and  maxilla,  the  nasal  cavity  and  its  ac- 
cessory sinuses,  may  be  radiographed  by  passing  the 
rays  directly  through  the  skull,  as  shown  in  Figs.  54  and 
55.  In  this  instance,  the  shadow  of  the  spine  will  be 
superimposed  upon  the  dental  structures,  but  owing  to 
the  fact  that  it  is  so  far  removed  from  the  plate,  its 
shadow  does  not  interfere  seriously.  It  is  important,  in 
making  these  pictures,  to  have  the  patient's  head  sup- 
ported in  such  a  manner  that  it  can  be  held  still  for  a 


DENTAL   AND    ORAL   RADIOGRAPHY   TECHNIC 


107 


longer  period  than  is  required  in  making  the  exposures 
of  the  other  areas  mentioned. 

When  ready  to  make  the  exposure  for  extra-oral  radio- 
grams, the  apparatus  is  arranged  with  the  anode  of  the 
tube  about  twenty  inches  from  the  plate.     The  patient 


Fig.  55. — In  following  out  the  teclinic  illustrated  in  Fig.  54,  the  patient's  head 
may  be  supported  by  a  bandage  of  gauze  of  necessary  to  secure  more  complete  im- 
mobility. 

is  instructed  to  heep  the  mouth  closed  with  the  teeth 
together  in  their  natural  occlusion.  They  should  also  be 
warned  as  to  the  approximate  length  of  time  the  ex- 
posure will  require,  and  that  they  must  remain  perfectly 
quiet. 


108  DENTAL   AND   ORAL   RADIOGRAPHY 

With  the  more  powerful  types  of  apparatus,  extra-oral 
radiograms  require  but  short  exposures,  but  if  an  oper- 
ator does  not  possess  high  power  apparatus,  he  should 
not  hesitate  to  use  this  method,  as  a  patient  properly 
seated  and  supported,  as  shown  in  Fig.  47,  can  easily  re- 
main quiet  for  five  or  ten  seconds,  or  perhaps  even  longer, 
should  it  be  necessary. 

In  making  a  complete  radiographic  examination  of  the 
teeth,  the  maxilla  and  mandible,  the  author  suggests  the 
following  procedure.  Extra-oral  radiograms  should  be 
made  of  each  side,  using  the  technic  illustrated  in  Figs. 
48,  49,  and  53.  This  would  mean  two  plates  for  each 
side.  Then  by  the  use  of  intra-oral  films,  the  region  ly- 
ing between  the  cuspids  both  above  and  below,  should  be 
radiographed.  These  plates  and  films  should  then  be 
developed  and  examined.  If  the  procedure  has  been  car- 
ried out  with  due  regard  for  all  the  elements  involved, 
the  result  should  constitute  a  general  radiographic  sur- 
vey of  the  teeth,  the  maxilla  and  the  mandible.  Should 
any  of  the  plates  or  films  exposed  fail  to  result  in  good 
radiograms,  additional  exposures  should  be  made,  as 
nothing  but  good  radiograms  should  be  depended  upon 
for  diagnosis. 

It  is  sometimes  advisable  after  making  a  complete  radi- 
ographic examination  by  the  method  just  advocated,  ' '  to 
check  up"  the  findings  of  extra-oral  radiograms  by  the 
use  of  the  intra-oral  films.  For  instance,  suppose  a  large 
plate  shows  what  appears  to  be  a  dento-alveolar  abscess 
upon  the  root  of  an  upper  bicuspid  or  molar  tooth.  An 
intra-oral  radiogram  of  this  particular  area  will  often 
settle  an}"  doubts,  as  a  higher  degree  of  detail  can  often 
be  obtained  by  concentrating  upon  the  small  area  in 
question. 

The  author  would  not  wish  to  imply  by  the  preced- 
ing remarks  upon  technic,  that  the  few  rules  enumerated 


J 


DENTAL   AND    ORAL   RADIOGRAPHY   TECHNIC  109 

constitute  a  safe  and  never  failing  means  of  producing 
good  radiograms.  There  are  many  points  to  be  consid- 
ered which  cannot  be  included  in  so  limited  a  text,  but 
which  must  be  learned  in  the  school  of  experience,  such 
as  the  necessary  variations  from  the  given  rules  of  tech- 
nic  because  of  anatomic  variations  in  the  dental  and  oral 
structures  of  patients.  Therefore,  the  rules  of  technic 
which  have  been  presented  must  be  accepted  only  in  the 
light  of  principles. 


CHAPTER  VIII 

TECHNIC  OF  DENTAL  AND  ORAL  RADIOGRAPHY 

(Continued) 

Successful  radiography  depends  upon  a  sequence  of 
operations,  each  of  which  must  be  carried  out  with  scien- 
tific accuracy.  These  steps,  upon  which  the  finished  prod- 
uct depends,  may  be  enumerated  as  follows : 

1st — Correct  technic  of  position. 
2nd — Proper  tube  and  current  conditions. 
3rd — Correct  exposure  and  development  of  plates  and 
films. 

It  would  be  difficult  to  determine  which  of  these  steps 
is  the  most  important ;  in  fact,  they  are  all  so  important 
that  a  radiogram  is  a  success  or  failure  in  accordance  with 
the  degree  of  accuracy  with  which  each  is  carried  out. 
In  the  preceding  chapter,  the  actual  technic  of  radiog- 
raphy, so  far  as  the  arrangement  of  apparatus  is  con- 
cerned and  its  relative  position  to  the  patient  and  the 
plate  (or  film),  has  been  discussed.  We  will,  therefore, 
proceed  to  the  next  factor  for  consideration. 

Proper  Tube  and  Current  Conditions 

The  character  of  the  x-rays  produced  in  a  tube  de- 
pends upon  the  degree  of  its  vacuum  and  the  current 
which  passes  through  it.  We  know  that  the  x-rays  are 
produced  by  the  cathode  stream  striking  the  anode  or 
target,  and  that  this  cathode  stream  (Fig.  57-M)  is  gen- 
erated by  the  flow  of  the  current  in  the  tube.  The  veloc- 
ity of  the  cathode  stream  depends  upon  the  voltage  of 
the  current  entering  the  tube,  therefore,  the  higher  the 

110 


DENTAL   AND    ORAL   RADIOGRAPHY   TECHNIC  111 

voltage,  the  faster  the  cathode  stream  travels,  and  the 
more  intense  or  penetrating  are  the  x-rays  produced. 
The  quantity  of  x-rays  produced  depends  upon  the  mil- 
liamperage  of  the  current. 

In  considering  the  role  enacted  by  the  voltage  and  mil- 
liamperage  in  the  x-ray  production,  we  have  assumed 
that  the  tube  is  exhausted  to  a  high  degree  of  vacuum, 
for  the  degree  of  vacuum  determines  to  a  large  extent, 
the  value  of  the  other  two  factors.  It  is  highly  important 
therefore  that  a  uniform  degree  of  vacuum  be  maintained 
so  that  all  the  factors  for  proper  x-ray  production  shall 
be  known  to  the  operator.  The  degree  of  vacuum  of  a 
tube  is  designated  as  high,  medium,  or  low,  a  ''high 
tube"  being  one  in  which  the  vacuum  is  well  nigh  com- 
plete; in  a  "medium  tube"  the  vacuum  is  less  complete, 
while  a  "low  tube"  is  one  in  which  the  vacuum  is  far 
from  complete. 

For  dental  radiography  a  medium  or  a  fairly  high  tube 
is  indicated,  as  with  such  a  tube  x-rays  may  be  produced 
having  a  degree  of  penetration  sufficient  to  pass  through 
the  oral  structures  and  produce  the  desired  effect  upon 
the  emulsion  of  the  plate  or  film. 

When  a  current  of  high  voltage  and  proper  milliam- 
perage  is  passed  through  an  ordinar}^  gas  tube  whose 
vacumn  is  "medium"  or  "fairly  high"  it  should  light 
up  in  a  characteristic  manner  forming  two  hemispheres 
which  have  a  definite  line  of  demarcation.  The  hemi- 
sphere in  front  of  the  target  which  is  the  active  hemi- 
sphere, is  evident  by  a  fluorescence  deep  apple  green  in 
color,  while  the  other  hemisphere  should  be  evident  by 
a  lack  of  greenish  light. 

To  Determine  the  Vacuum  of  a  Tube 

The  comparative  degree  of  vacuum  of  a  tube  can  be 
determined  in  the  following  mariner:    Connect  the  tube 


112 


DENTAL   AND   ORAL   RADIOGRAPHY 


to  the  X-ray  machine  as  shown  in  Fig.  56.  See  that  the 
third  terminal  {S')  is  moved  well  away  from  the  nega- 
tive terminal  (S),  or  better  still,  disconnect  the  wire  run- 
ning to  the  regulation  chamber  (R).  Now,  move  the 
sliding  rods  {B  and  D)  of  the  secondary  spark  gap,  to- 
ward each  other  until  they  are  about  three  inches  apart, 
and  start  the  current.  Unless  the  tube  is  loiv,  the  cur- 
rent will  jump  the  spark  gap  instead  of  passing  through 
the  tube.    If  the  tube  resists  the  current  and  causes  it 


Fig.    56.       -, 

to  jump  the  spark  gap,  it  is  said  to  have  *' backed  up" 
three  inches  of  spark.  Thus  a  "low  tube"  will  back  up 
two  or  three  inches  of  spark,  a  "medium  tube"  five  or 
six  inches,  while  a  high  tube  will  back  up  six  or  eight 
inches.  In  fact,  the  vacuum  of  a  tube  may  be  so  great 
that  only  the  most  powerful  x-ray  machines  will  operate 
it.  Such  a  tube,  however,  is  not  useful  for  dental  radiog- 
raphy. 

The  vacuum  of  a  tube  may  also  be  determined  by  the 
use   of   an  instrument  known  as   a  milliamperemeter. 


DENTAL   AND    ORAL   RADIOGRAPHY   TECHNIC  113 

This  instrument  which  is  usually  an  accessory  of  either 
the  induction  coil  or  transformer,  is  connected  in  circuit 
with  the  tube,  and  measures  the  current  passing  through 
the  tube.  "With  a  "low  tube"  the  milliamperemeter  will 
show  a  reading  of  15  to  18,  while  with  a  "medium  tube" 
the  reading  will  be  from  10  to  12,  and  with  a  "high  tube" 
the  milliamperemeter  will  register  5  or  less. 

Relative  Merits  of  Low,  Medium,  and  High  Tubes 

A  ' '  low  tube ' '  in  operation  under  average  current  con- 
ditions gives  a  clear  sharp  hemisphere  of  pale  greenish 
in  front  of  the  target,  with  usually  a  trace  of  bluish 
light  in  the  region  of  the  assistant  anode.  If  the  tube 
is  very  low  the  cathode  stream  shows  blue,  and  there  is 
a  bluish  light  back  of  the  active  hemisphere.  Such  a 
tube  will  not  do  good  radiographic  work,  as  the  x-rays 
produced  l)y  it  are  lacking  in  penetration. 

A  "medium  tube"  gives  a  clear,  sharp  hemisphere  of 
light  greenish  color,  and  there  is  an  absence  of  bluish 
light  back  of  the  target.  The  rays  emanating  from  such 
a  tube  are  more  penetrating  than  those  from  the  "low 
tube,"  but  are  not  so  well  suited  for  "bone  radiography" 
as  those  which  come  from  a  tube  fairly  high  in  vacuum. 
When  such  a  tube  is  operating,  it  gives  a  clear  sharp 
hemisphere  deep  apple  green  in  color,  with  a  lack  of 
greenish  light  back  of  the  target.  The  x-rays  emanat- 
ing from  such  a  tube  are  of  degree  of  penetration  ivhicJi 
is  best  buited  for  bone  radiograpliy,  for  they  penetrate 
and  pass  through  the  soft  tissues  and  to  a  sufficient  de- 
gree through  the  bone  structure  to  give  good  contrast. 

It  is  very  important  that  the  vacuum  of  such  a  tube 
be  kept  uniform,  for  if  it  becomes  lowered,  the  power  of 
penetration  of  the  rays  is  decreased,  and,  on  the  other 
hand,  if  the  vacuum  gets  too  high,  the  penetrating  power 
of  the  rays  will  be  increased.     Variation  either  up  or 


114  DENTAL   AND   ORAL   RADIOGRAPHY 

down  is  unfortunate  as  it  makes  it  impossible  for  the 
operator  to  proceed  with  any  assurance  of  uniform 
results. 

Regulating  the  Tube 

Prior  to  seating  and  arranging  the  patient,  the  tube 
if  it  be  of  the  gas  type  should  be  tested  out  and  any 
needed  change  in  its  vacuum  effected.  This  is  easily  ac- 
complished by  utilizing  the  third  terminal  of  the  x-ray 
machine.  The  tube  should  be  connected  to  the  machine 
as  shown  in  Fig.  56.  The  terminals  of  the  regulating 
spark  gap  (S'S)  should  be  placed  about  four  inches 
apart,  and  the  current  (of  correct  working  strength) 
turned  on  for  an  instant.  If  a  line  of  sparks  jump  be- 
tween S'  and  S,  it  shows  the  vacuum  of  the  tube  is  too 
high.  In  this  even  the  regulating  spark  gap  (S'S) 
should  be  reduced  to  about  two  inches,  and  a  small 
amownt  of  current  turned  on.  This  weaker  current  will 
pass  across  the  spark  gap  {S'S),  travel  do^^^l  the  wire 
connected  to  the  regulating  chamber,  and  by  heating  the 
abestos  (impregnated  with  chemicals),  will  liberate 
enough  gas  to  reduce  the  vacuum.  Unless  the  tube  is 
very  high,  a  few  seconds  will  suffice  to  reduce  it  to  the 
vacuum  desired.  To  be  sure  the  vacuum  is  right,  the 
regulating  spark  gap  {S'S)  should  be  widened  to  about 
four  inches,  and  the  desired  working  current  again 
passed  through  the  tube  for  an  instant.  If  the  tube 
lights  up  with  a  clear  sharp  active  hemisphere  deep  apple 
green  in  color  with  a  lack  of  greenish  light  back  of  the 
target,  and  if  it  carries  the  desired  amount  of  working 
current,  3'ou  then  know  it  is  ready  for  work. 

If  an  x-ray  machine  is  not  equipped  with  a  third  termi- 
nal, the  same  results  in  regulating  the  tube  may  be  ef- 
fected by  using  the  regulating  adjuster  (Fig.  57),  the  end 
of  which  can  be  placed  at  the  desired  distances  from 


DENTAL   AND    ORAL   RADIOGRAPHY   TECHNIC 


115 


negative  wire  near  its  point  of  attachment  to  the  tube. 
The  tube  may  also  be  lowered  by  attaching  the  negative 
wire  directly  to  the  regulating  chamber  and  passing  a 
small  amount  of  current  through  the  circuit. 

These  manipulations  should  be  carried  out  with  the 
greatest  caution,  for  a  tube  is  an  extremely  delicate  and 
sensitive  piece  of  apparatus  and  ivill  not  stand  abuse. 

A  careless  operator  can  quite  easily  reduce  the  vac- 
uum to  such  a  degree  that  the  tube  is  useless.  Such  a 
tube  has  a  purple  appearance  when  the  current  is  passed 
through  it.     If  such  a  tube  has  not  been  too  greatly 


A — Anode. 
U--Assislanl  Anortc 
C— Calliodf 
D— Rfsulalini; 

Chanibir 
P-Rcgula.int:      ^.l 

juslcr 
G— HrtnlspluK- 
H — Connpctimi 

Wire 
I— ^ssisunc    Anr.ilc 

tap 
K  — Anode   Cap 
L — Calhodr    Cap 
M— Caihodr  Sitrain 
N— Focal    I'oini 


abused,  it  will  often  regain  its  vacuum  if  given  a  rest.  If 
this  does  not  bring  the  vacuum  up,  it  can  often  be  brought 
back  in  the  following  way:  The  spiral  spring  (Fig.  57) 
connecting  the  anode  and  assistant  anode  should  be  re- 
moved and  the  positive  wire  from  the  machine  attached 
to  the  assistant  anode  (7).  The  negative  wire  is  at- 
tached as  usual  (at  L)  and  a  light  current  is  run  through 
the  tube  for  a  minute  or  two  at  a  time.  If  this  is  done 
once  or  twice  a  day  for  several  days,  the  vacuum  will 
usually  come  up.  Any  increase  in  vacuum  will  be  indi- 
cated by  the  milliampere  readings  dropping  off,  or  by 


116 


DENTAL   AND   ORAL   RADIOGRAPHY 


the  increased  length  of  spark  gap  the  tube  will  "back 
up." 

If  a  tube  does  not  respond  to  this  treatment  but  con- 
tinues to  be  purple  Avhile  operating,  it  indicates  that  it 
is  practically  nonvacuous  or  ''punctured."  It  is  then 
useless  and  should  be  sent  back  to  the  manufacturer  for 
repairs.  In  the  event  a  tube  is  ''completely  punctured," 
the  current  in  passing  through  it  simply  jumps  the  gap 
between  the  anode  and  cathode,  and  is  evident  as  a  line 
of  white  sparks. 

One  tube  complication  not  3^et  mentioned  is  sometimes 
encountered  in  the  use  of  induction  coils.    This  is  known 


l-'ig.   58. — Radiator  tyi)e   Coolidge  tube. 


Fig.   59. — Radiator  Coolidge   tube,   right   angle   type. 

as  "inverse  in  the  tube,"  and  is  the  result  of  the  pres- 
ence of  inverse  current  (current  in  the  wrong  direction) 
in  the  secondary  circuit  of  the  coil.  "Inverse"  is  evi- 
dent in  the  tube  by  the  appearance  of  rings  of  light  back 
of,  and  usually  running  at  an  angle  to,  the  active  hemi- 
sphere, or  by  a  fullness  of  greenish  light  back  of  the  ac- 
tive hemisphere,  with  rings  about  the  assistant  anode. 
Inverse  current  in  a  tube  will  generate  secondary  rays 
which  have  the  tendency  to  make  the  outline  of  the  image 
on  the  plate  hazy  or  "less  sharp,"  as  these  rays  are  pro- 
duced in  the  tube  elsewhere  than  at  a  focal  point  on  the 


DENTAL    AND    ORAL    RADIOGRAPHY    TECHNIC  117 

target.  It  also  produces  heat  in  the  tube  which  lowers 
the  vacuum  and  hence  lessens  the  penetration  of  the  rays 
coming  from  it. 

"Inverse"  in  the  tube  can  usually  be  controlled  or  pre- 
vented by  the  use  of  '*a  multiple  spark  gap"  or  ''a  valve 
tube"  arranged  in  series  with  the  x-ray  tube,  and  by 
using  a  tube  which  is  fairly  high  in  vacuum.  If  it  still 
persists  after  these  precautions  are  taken,  it  indicates 
an  imperfect  adjustment  of  the  induction  coil  or  some  of 
its  accessories. 

All  manufacturers  of  x-ray  tubes  furnish  full  instruc- 
tions as  to  the  care  of  and  manner  of  using  x-ray  tubes. 
These  instructions  should  be  carefully  read  and  explic- 
itly follotved. 

In  order  that  uniform  results  may  be  obtained,  it  is 
advisable  to  always  use  the  tube  at  the  same  vacuum, 
with  the  same  amount  of  current.  The  proper  ' '  working 
current"  for  dental  and  oral  radiography  may  be  deter- 
mined in  the  following  way :  With  the  tube  disconnected, 
set  the  sliding  rods  {B  and  D  of  Fig.  56)  of  the  machine 
about  four  or  five  inches  apart.  Then  start  the  current 
in  the  machine,  and  beginning  with  a  low  current  in- 
crease it  until  a  fat  fuzzy  "caterpillar  spark"  is  pro- 
duced across  the  spark  gap.  As  soon  as  this  spark  or 
discharge  appears,  the  switch  should  be  pulled  out,  but 
the  rheostat  or  other  controlling  apparatus  left  as  it 
was  when  the  spark  appeared,  so  that  when  the  tube  is 
connected,  the  proper  working  current  will  come  from 
the  machine. 

The  tube  should  then  be  connected  up  and  given  a  trial. 
If  it  is  not  too  high  in  vacuum,  it  should  take  the  cur- 
rent, or  in  the  event  it  is  too  high,  it  will  "back  up"  the 
spark,  and  the  discharge  instead  of  passing  through  the 
tube  will  jump  the  gap.  If  the  tube  requires  regulating, 
it  can  be  done  by  the  methods  before  described. 


118  DENTAL   AND   ORAL   RADIOGRAPHY 

With  tlie  working  current  and  vacuum  established,  it 
is  a  good  idea  to  separate  the  sliding  rods  on  the  ma- 
chine to  at  least  eight  inches,  to  insure  against  the  tube 
backing  up  the  current,  for  in  the  event  the  tube  should 
start  going  up  during  the  time  the  exposure  is  being 
made,  the  startling  noise  made  by  the  discharge  jumping 
the  gap,  may  cause  the  patient  to  move  and  thereby  blur 
the  radiogram.  If  several  exposures  of  five  or  ten  sec- 
onds each  are  made,  the  tube,  if  it  be  a  gas  tube,  should 
be  given  sufficient  rest  between  exposures  so  that  it  will 
not  heat  up.     This  is  important. 

With  proper  tube  and  current  conditions,  the  length  of 
time  required  for  the  exposure  will  depend  somewhat 
upon  the  type  of  x-ray  macliine  used,  and  the  thickness 
and  density  of  the  parts  to  be  radiographed,  varying 
with  different  patients  according  to  age  and  structural 
make  up. 

In  order  that  uniform  and  dependable  radiograms 
shall  be  produced,  the  operator  sliould  adopt  a  technic  of 
tube  operation  suited  to  his  needs  aud  adhere  to  it.  If 
this  habit  is  acquired  early  it  will  be  found  that  the  re- 
quired exposure  for  any  given  case  will  after  a  little  ex 
perience  become  a  simple  matter. 

Such  a  technic  requires  the  selection  of  a  definite 
amount  of  ** spark  back  up'*  or  "working  current"  and 
the  use  of  a  definite  number  of  milliamperes  of  current 
passing  through  the  tube,  the  "back  up"  as  stated  before 
representing  the  voltage  or  pressure  of  the  current  and 
tlie  milliamperage  the  volume.  These  two  factors  when 
combined  with  uniform  tube  vacuum  make  possible  ac- 
curate and  definite  results,  provided  the  tube  is  operated 
at  the  same  distance  from  the  parts  being  radiographed. 
In  other  words,  a  definite  irorliuff  distance  must  he  main- 
tained if  residts  are  to  be  duplicated.  AVhile  different 
operators  have  preferences,  the  writer  has  found  it  ad- 


DEXTAL   AND   ORAL   RADIOGRAPHY   TECHXIC  119 

vantageous  to  keep  the  target  of  the  tube  approximately 
18  to  20  inches  from  the  plate  or  film.  If  this  factor  is 
varied,  the  intensity  of  the  rays  will  change  with  it  in 
definite  ratio,  for  they  will  vary  inversely  as  the  square 
of  the  distance  from  the  target  of  the  tube  to  the  plate 
or  film.  Thus  if  the  distance  is  doubled,  the  intensity  of 
the  rays  will  be  one-fourth  as  great  as  it  was  previously, 
or  if  the  distance  is  tripled,  the  intensity  will  be  but  one- 
ninth  as  great  as  at  the  original  distance,  etc. 

For  intra-oral  radiograms,  a  "spark  back  up"  of  four 
or  four  and  a  half  inches  with  twenty  milliamperes  will 
give  very  satisfactory  results.  If  extra-oral  radiograms 
are  to  be  made,  a  higher  degree  of  penetration  is  neces- 
sary and,  therefore,  five  or  even  six  inches  of  "spark 
back  up"  should  be  employed  either  with  the  same  milli- 
amperes (twenty)  or  with  an  increase  of  ten  or  even  fif- 
teen milliamperes  for  dense  objects. 

The  Use  of  the  Coolidge  Tube 

The  introduction  of  the  Coolidge  tube  has  proved  to 
be  the  greatest  addition  to  x-ray  equipment  of  recent 
years  for  it  has  made  possible  uniform  results  in  a  man- 
ner which  greatly  lessens  the  burdens  of  the  radiog- 
rapher. While  the  radiograms  produced  by  it  do  not 
exceed  in  excellence  those  made  with  other  tubes,  its  ease 
of  operation,  hardy  construction  and  never  varying  re- 
sults made  possible  l)y  its  perfect  control,  promise  to 
make  it  the  most  popular  of  all  x-ray  tubes. 

This  tube  is  built  and  operated  in  quite  a  different 
manner  from  the  ordinary  gas  tube.  (See  Figure  27). 
The  target  or  anode  is  smaller  and  is  constructed  en- 
tirely of  tungsten,  while  the  cathode  is  placed  well  out 
in  the  tube  but  a  short  distance  from  the  anode  and  con- 
sists of  a  spiral  filament  of  flat  closely  wound  tungsten 
wire  located  with  a  small  shell  or  short  metal  tube. 


120  DENTAL   AND   ORAL   RADIOGRAPHY 

The  tube  is  energized  by  two  distinct  currents,  one  cf 
high  voltage  Avhich  is  derived  fi'om  the  x-ray  machine, 
and  the  other  a  low  voltage  current  derived  from  a  stor- 
age battery  or  "step-down"  transformer.  The  object 
of  the  low  voltage  current  is  to  electrically  heat  the  spiral 
filament  in  the  cathode  for  the  filament  heat  governs  the 
amount  of  current  ivhich  can  pass  through  the  tube.  A 
rheostat  is  connected  in  series  with  the  filament  heat 
current  supply  as  well  as  an  ameter,  both  of  which  make 
possible  a  fine  degree  of  current  control  and  scale  read- 
ing so  that  the  filament  of  the  cathode  can  be  brought  to 
any  desired  heat  and  maintained  there. 

When  the  desired  amount  of  "voltage"  or  "working 
current"  or  "back  up"  has  been  determined  as  well  as 
the  milliamperage  to  be  used  for  the  character  of  work 
at  hand  the  filament  current  is  turned  on  and  the  cathode 
heated  to  the  point  where  the  tube  will  take  the  current. 
AMien  this  is  once  done  and  the  meter  readings  of  the 
"Coolidge  control"  (the  apparatus  governing  the  heat- 
ing of  the  filament)  noted  as  well  as  the  milliamper- 
meter  on  the  machine,  it  is  only  necessary  on  subsequent 
occasions  to  set  the  controls  at  the  same  points  and  pro- 
ceed. 

The  vacuum  of  this  tube  does  not  undergo  change  as 
the  milliamperage  of  the  current  which  passes  through 
it  is  governed  absolutely  by  the  filament  heat,  the  higher 
the  heat  the  larger  the  number  of  milliamperes  will  flow 
through  the  tube  and  consequently  the  shorter  will  be 
the  exposure  required  to  produce  the  desired  elTect  upon 
the  photographic  emulsion. 

Owing  to  the  fact  that  the  flow^  of  the  current  is  con- 
trolled so  positively,  this  tube  may  be  used  for  repeated 
exposures  or  in  fact  it  may  be  used  for  hours  if  necessary 
Avithout  its  vacuum  being  affected,  which  would  of  course 
be  impossible  with  any  other  type  of  tube.     From  the 


DENTAL   AND    ORAL   RADIOGRAPHY    TECHNIC  121 

standpoint  of  durability  it  is  in  a  class  by  itself,  its 
length  of  life  being  practically  without  limit  providing  it 
is  not  roughly  handled  and  broken. 

There  are  two  distinct  types  of  Coolidge  tubes,  the 
first  of  which  is  kno^\^l  as  the  ' '  universal  type ' '  and  the 
other  as  the  "radiator  type."  The  universal  type  is  the 
older  of  the  two  and  has  proven  highly  satisfactory  for 
general  all  around  usage.  It  is  obtainable  with  a  broad, 
medium  and  fine  focus,  the  term  ' '  focus ' '  referring  to  the 
area  upon  the  anode  from  which  the  x-rays  emanate.  As 
a  high  degree  of  detail  is  necessary  in  dental  and  oral 
radiography  a  fine  focus  tube  is  preferable  for  our  use. 
Such  a  tube  should  be  energized  by  an  interrupterless 
transfoniier  with  the  addition  of  the  special  Coolidge 
control  apparatus  which  has  already  been  mentioned  and 
described. 

Coolidge  tubes  of  the  "radiator  type"  while  similar 
in  principle  are  different  in  several  respects  from  the 
"universal  type."  They  are  energized  by  an  x-ray  ma- 
chine which  is  a  "step-up  transformer"  but  has  no  recti- 
fying switch  such  as  is  employed  in  the  interrupterless 
transformer.  This  apparent  discrepancy  is  overcome  by 
the  tube  itself  which  in  addition  to  its  other  functions 
rectifies  the  current.  The  filament  of  the  cathode  is 
heated  from  a  "step-down"  transformer  arranged  in 
conjunction  with  the  machine,  all  of  which  makes  possible 
a  very  compact  unit  which  gives  promise  of  becoming 
very  popular  especially  where  but  a  small  amount  of 
space  can  be  given  up  to  x-ray  equipment. 

Radiator  tubes  are  made  in  both  straight  and  right 
angle  form  as  shown  in  Figs.  58  and  59  and  as  stated 
before  they  must  be  operated  on  machines  especially 
adapted  for  them.  Such  outfits  or  "step-up  transformer 
units"  are  usually  operated  with  a  set  amount  of  "spark 
bach  up"  and  current  milliamperage.    This  is  made  nee- 


122 


DENTAL   AND   ORAL   RADIOGRAPHY 


essary  by  the  fact  that  such  tubes  are  limited  in  the 
amount  of  current  they  will  rectify.  Such  units  are 
usually  made  in  two  sizes,  the  smaller  of  which  operates 
with  three  inches  of  spark  back  up  and  ten  milliamperes 
of  current,  while  the  other  operates  wdth  five  inches  of 
spark  back  up  and  has  a  capacity  of  thirty  milliamperes 
of  current. 

While  they  no  doubt  give  excellent  service  for  certain 
classes  of  work  they  cannot  be  regarded  as  flexible  or 
powerful  as  the  interrupterless  transformer  with  a  va- 
riable spark  back  up  used  in  conjunction  wdth  the  uni- 
versal type  of  Coolidge  tube. 


CHAPTER  IX 

CORRECT  EXPOSURE  AND  DEVELOPMENT  OF 
X-RAY  PLATES  AND  FILMS 

X-ray  plates  and  films  differ  from  those  used  in  or- 
dinary photography  in  that  their  emulsion  is  more  sen- 
sitive and  better  adapted  to  record  the  shadows  produced 
by  the  x-ray.  Therefore,  they  should  always  be  used  in 
preference  to  ordinary  plates  and  films. 

The  same  general  photographic  rules  apply  to  x-ray 
plates  and  films  as  apply  to  the  ordinary  kind,  except 
perhaps  that  they  demand  a  greater  degree  of  accuracy 
and  care  throughout  the  process  of  exposure  and  devel- 
opment, if  the  very  best  results  are  to  be  obtained. 

X-ray  Plates 

X-ray  plates  are  supplied  by  the  manufacturers,  packed 
in  lightproof  boxes  containing  one  dozen  plates.  They 
are  obtainable  in  any  desired  size,  but  for  dental  and 
oral  radiography,  a  5x7  plate  is  large  enough.  If  stored 
in  the  laboratory,  they  should  be  kept  in  a  lead-lined  box 
prior  to  their  preparation  for  exposure,  or  they  will  be- 
come *' fogged,"  as  lightproof  boxes  offer  no  protection 
whatever  from  the  x-ray. 

A  suitable  plate  and  film  storage  box  is  shown  in  Fig. 
60.  Such  a  box  should  be  about  twelve  inches  square 
and  five  inches  deep.  This  will  enable  the  storage  of 
several  boxes  of  5x7  plates,  and  in  addition,  three  or  four 
dozen  dental  films. 

In  their  preparation  for  exposure,  each  plate  is  placed 
in  two  lightproof  envelopes,  one  of  which  is  black  and 
the  other  red  or  orange  in  color.    Such  envelopes  are 

123 


124 


DENTAL    AND    ORAL    ItADIOGllAPH Y 


furnished  by  plate  manufacturers  and  are  obtainable  in 
the  desired  size.  The  transference  of  the  plate  from  its 
original  box  to  the  envelopes  must,  of  course,  only  he  done 
in  the  photographic  darkroom.  The  plate  is  first  slipped 
into  the  smaller  envelope  which  is  usually  the  black  one, 
with  the  emulsion  side  of  the  plate  facing  the  smooth 
side  of  the  envelope  (the  side  free  from  seams  or  over- 
lapping edges).  The  envelope  containing  the  plate  is 
then  placed  in  the  larger  or  yellow  envelope,  flap-end 
first,  with  the  smooth  side  of  the  inner  envelope  facing 
the  smooth  side  of  the  outer  one.     Plates  prepared  in 


Fig.   50. — X-rayproof   film   and   plate   chest. 

this  way  are  then  ready  for  exposure  and  can  be  placed 
back  in  the  lead-lined  box  until  needed. 

In  "loading  these  envelopes,"  care  should  be  taken 
lest  the  emulsion  of  the  plate  become  scratched,  as 
scratches  even  though  they  be  very  slight  will  often  cur- 
tail the  value  of  the  finished  radiogram. 

It  is  not  advisable  to  keep  large  quantities  of  plates 
loaded  in  envelopes,  unless  they  are  to  be  used  within  a 
few  days,  as  the  contact  of  the  paper  with  the  emulsion 
will  in  time  affect  it  adversely. 

All  "brands"  of  x-ray  plates  are  not  the  same,  there- 
fore, if  the  best  results  are  obtained  in  using  any  par- 
ticular kind,  they  must  be  handled  in  strict  accordance 


DEVELOPMENT    OF    PLATES   AND    FILMS  125 

with  the  manufacturers'  instructions.  For  dental  and 
oral  radiography,  a  plate  should  be  fairly  rapid  (that  is, 
it  should  not  require  a  long  exposure),  give  a  high  de- 
gree of  detail  and  good  contrast,  and  should  be  uniform 
in  its  reaction  to  the  x-ray. 

X-ray  Films 

In  making  intra-oral  radiograms,  a  film  is  preferable 
to  a  plate  as  it  is  flexible  and,  therefore,  can  be  more 
easily  adapted  to  the  inside  of  the  mouth.  These  films 
are  obtainable  in  several  convenient  sizes,  wrapped  in 
lightproof  and  dampproof  coverings  ready  for  exposure. 
Like  plates  they  should  be  kept  in  a  lead-lined  box  for 
protection. 

With  these  "dental  films"  as  they  are  called,  you  have 
the  choice  of  two  different  emulsions,  one  of  which  is 
much  more  ''rapid"  than  the  other. 

The  ''rapid"  or  "fast  film"  requires  only  about  one- 
fourth  or  one-third  as  long  an  exposure  as  the  ' '  regular ' ' 
or  "slow  film,"  and  therefore  is  an  advantage  to  the 
radiographer  who  uses  one  of  the  less  powerful  types 
of  x-ray  machines.  However,  such  a  film  does  not  have 
as  much  latitude  as  the  slow  film,  and  is  therefore  more 
easily  overexposed.  If  properly  exposed,  either  one  will 
give  satisfactory  results. 

When  arranging  a  plate  or  film  for  exposure,  the  emul- 
sion side  should  lie  next  to  the  structures  being  radio- 
graphed. If  this  rule  is  systematically  followed,  it  is  an 
easy  matter  to  identify  radiograms,  i.  e.,  whether  they 
represent  structures  on  the  right  or  left  side  of  the  me- 
dian line. 

The  Exposure  of  the  Plate  or  Film 

The  actual  time  required  to  properly  expose  a  plate 
or  film  depends  upon  several  factors  as  has  already  been 


126  DENTAL   AND   ORAL   RADIOGRAPHY 

made  plain  in  the  discussion  of  tube  and  current  condi- 
tions. Assuming  that  the  before  mentioned  conditions 
are  kno^^^l  to  the  operator  and  are  under  control,  the 
next  factors  for  consideration  are  the  character  of  the 
emulsion  of  the  plate  or  film  being  used  and  the  density 
of  the  parts  through  which  the  x-rays  must  penetrate. 

It  is  well  for  the  beginner  in  this  work  to  use  standard 
plates  and  films  of  known  ''speed"  and  the  slow  variety 
is  recommended.  After  becoming  thoroughly  familiar 
with  these  it  will  not  be  difficult  for  the  operator  to 
modify  his  technic  to  handle  the  other  varieties. 

The  vast  majority  of  exposures  may  be  figured  as  re- 
quiring an  average  amount  of  time  especially  if  they  are 
being  made  of  adult  patients.  Young  children  of  course 
require  shorter  exposures  than  adults  and  those  cases 
among  adults  where  the  patients  are  thick  and  heav}"  and 
show  evidence  of  strong  osseous  dev^elopment  will  re- 
quire a  little  longer  exposure  than  the  average.  Judg- 
ment in  this  matter  as  well  as  in  other  phases  of  this 
work  will  naturally  come  Avith  experience. 

Many  operators  prefer  to  figure  their  exposures  in 
"milliampere  seconds."  Under  known  tube  and  current 
conditions  a  "milliampere  second"  is  one  milliampere  of 
current  passing  through  the  tube  for  one  second.  Let  us 
suppose  therefore  that  with  a  certain  speed  of  plate  or 
film,  the  exposure  required  for  the  average  patient  is 
eighty  milliampere  seconds.  If  ten  milliamperes  are  be- 
ing passed  through  the  tube  the  required  exposure  would 
be  eight  seconds.  If  twenty  milliamperes  are  being 
utilized,  four  seconds  will  be  required,  etc. 

Not  infrequently  manufacturers  of  plates  and  films 
for  dental  and  oral  radiography  include  among  their  in- 
structions and  suggestions  the  approximate  number  of 
milliampere  seconds  required  for  proper  exposure.  Such 
instructions  should  be  carefully  followed  for  they  will 


DEVELOPMENT    OF    PLATES   AND    FILMS  127 

oftentimes  save  the  operator  the  necessity  of  determin- 
ing the  time  factor  by  experiment. 

Intra-oral  radiograms  of  the  lower  teeth  usually  re- 
quire less  time  than  is  required  to  expose  the  upper  teeth, 
as  the  mass  of  the  tissues  to  be  penetrated  is  not  so  great. 
Of  the  upper  teeth  the  molars  require  the  longest  ex- 
posure as  the  x-ray  must  penetrate  a  greater  distance 
before  reaching  the  emulsion. 

In  making  intra-oral  exposures  the  author  uses  the 
same  milliamperage  and  ''spark  back  up"  for  both  the 
upper  and  lower  teeth  but  varies  the  time  slightly  as  sug- 
gested above  and  has  found  the  method  very  satisfactory. 
For  such  work  twenty  milliamperes  of  current  with  four 
or  four  and  a  half  inches  of  "spark  back  up"  are  used. 
For  intra-oral  work  where  children  are  the  subjects  for 
exposure  the  factors  are  kept  the  same  but  for  adults 
the  "spark  back  up"  is  increased  to  five  or  even  six 
inches  and  the  milliamperage  increased  to  thirty  as 
added  penetration  and  volume  are  needed. 

Development  of  Plates  and  Films 

The  process  of  "development"  of  either  plates  or 
films  may  be  briefly  described  as  follows:  At  a  con- 
venient time  following  the  "exposure,"  the  plate  or 
plates  (or  films)  are  taken  into  the  "darkroom."  Such 
a  room  has  all  white  light  excluded  from  it,  and  is  illu- 
minated only  by  a  so-called  "ruby  light"  or  darkroom 
lantern.  The  darkroom  should  be  supplied  with  a  shelf 
or  table  about  two  and  a  half  feet  wide  and  three  feet 
long  placed  at  ordinary  table  height  from  the  floor,  so 
that  the  operator  may  sit  upon  a  stool  while  at  work. 
Upon  this  shelf  there  should  be  four  trays,  one  for  the 
"developing  solution,"  one  for  the  "fixing  bath,"  and 
the  other  two  for  water.    Where  a  darkroom  is  supplied 


128  DENTAL   AND   ORAL   RADIOGRAPHY 

with  running  water  and  a  sink,  only  three  trays  are  nec- 
essary. 

"With  all  light  excluded  from  the  room  except  the  ruby 
light  coming  from  the  darkroom  lantern,  the  plate  (or 
film)  is  taken  out  of  its  envelope  and  immersed  emulsion 
side  up  in  the  devoloping  solution.  In  order  to  insure  a 
uniform  action  by  the  developer,  the  tray  should  be  fre- 
quently rocked  with  a  gentle  motion.  If  the  plate  (or 
film)  has  been  properly  exposed,  development  should  be 
complete  in  about  five  minutes  (although  the  time  varies 
with  different  formulae). 

The  plate  or  film  is  then  removed  from  the  developer 
and  placed  in  a  tray  of  water  to  thoroughly  wash  the 
developing  solution  from  it.  This,  of  course,  requires 
but  a  moment,  and  it  is  then  immersed  in  the  **  fixing 
bath,"  keeping  the  emulsion  side  up.  As  soon  as  the 
plate  has  been  in  the  fixing  bath  a  few  seconds,  the  dark- 
room door  may  be  opened  and  light  admitted  without  in- 
jurious effects.  However,  the  plate  (or  film)  must  still 
remain  in  the  fixing  bath  until  it  has  ''cleared"  (until 
all  milkiness  is  gone  from  the  back  of  the  plate),  which 
will  usually  require  from  five  to  ten  minutes.  In  fact, 
it  is  better  to  let  it  "fix"  for  at  least  five  minutes  longer 
than  is  required  for  it  to  become  clear. 

When  the  fixing  process  is  complete,  the  plate  must  be 
placed  in  water  and  thoroughly  washed  to  remove  all  the 
fixing  solution  from  it.  This  can  be  accomplished  by 
washing  it  in  several  changes  of  water,  or  better  still, 
place  it  in  a  basin  or  tray  of  cold  "running  water"  for 
ten  or  fifteen  minutes. 

When  the  washing  process  is  complete,  the  emulsion 
side  of  the  plate  or  film  should  be  gently  rubbed  with  a 
clean  piece  of  wet  cotton,  holding  the  plate  (or  film) 
under  a  cold  water  faucet  during  the  act.  The  developed 
radiogram  is  then  ready  to  dry.    Plates  should  be  stood 


DEVELOPiMENT    OF    PLATES   AND    FILMS  129 

on  edge  or  placed  in  a  suitable  rack  so  that  nothing  will 
come  in  contact  with  the  emulsion  side,  and  left  until 
l^erfectly  dry.  Films  may  be  pinned  to  the  edge  of  a 
shelf,  or  secured  to  a  line  with  suitable  clips.  The  drying 
process  should  take  place  in  a  room  free  from  dust  or 
soot,  for  these  will  prove  injurious  to  the  drying  emulsion. 

The  size  of  the  traj^s  used  in  the  darkroom  will  depend 
upon  the  number  of  plates  or  films  which  are  to  be 
carried  through  the  developing  process  at  a  time.  For 
plates,  the  author  uses  trays  8x10  inches  in  size.  With 
such  trays  two  5x7  plates  can  be  carried  through  at  a 
time.  Where  a  large  number  of  plates  are  being  devel- 
oped, additional  trays  can  be  used  and  if  necessary 
'Hanks"  capable  of  holding  a  dozen  plates,  utilized  in 
the  fixing  or  washing  process.  In  developing  ''dental 
films, ' '  small  trays  will  be  found  convenient,  and  unless  a 
large  number  are  to  be  developed  at  a  time,  a  4x5  or  5x7 
tray  will  be  large  enough. 

Trays  should  be  labeled  according  to  the  purpose  for 
which  they  are  to  be  used,  and  used  for  that  purpose 
only.  Tliat  is,  developing  trays  should  be  used,  for  the  de- 
veloper only,  and  fixing  trays,  only  for  the  fixing  bath, 
if  troublesome  chemical  reactions  are  to  be  avoided. 

Any  one  of  several  good  formulae  may  be  used  in  the 
developing  and  fixing  process.  The  following  has  given 
satisfactory  results  in  the  hands  of  the  author,  and  is 
easily  prepared: 

Developer 

Water  (distilled)  ■   20  oz. 

Metol  20  gr. 

Hydroquinone  80  gr. 

Sodium  sulphite   (dry)  1  oz. 

Sodium  carbonate  (dry)  1  oz. 

Potassium  bromide  10  gr. 


130  DENTAL   AND   ORAL   RADIOGRAPHY 

Fixing  Bath 


Solution  A: 

J 

Water  (distilled) 

30  oz.                     1 

Hyposulphite  of  soda 

1  lb.                     j 

Solution  B: 

' 

Water  (distilled) 

15  oz. 

Chrome  alum 

1  oz.                     1 

Sodium  sulphite  (dry) 

2  oz.                      1 

Solution  C: 

1 

Water   (distilled) 

5  oz.                     1 

Sulphuric  acid  (C.P.) 

Vs  oz.                      9 

Add  C  to  B  (when  cold)  and  the  mixed  solutions  to  A. 

If  the  best  results  are  to  be  obtained  in  developing, 
the  temperature  of  the  solution  should  be  kept  between 
65°  and  75°  F.  If  the  temperature  gets  much  over  75°, 
the  plate  will  develop  too  fast,  while  if  the  temperature 
goes  much  below  65°,  development  will  be  retarded. 

It  is  a  mistake  to  try  to  develop  a  large  number  of 
plates  with  the  same  mixture  of  developer,  for  after  it 
has  developed  a  half  dozen  plates,  it  will  become  weak 
and  not  give  the  best  results.  Therefore,  do  not  hesitate 
to  use  plenty  of  fresh  developer  if  you  expect  to  get  satis- 
factory results. 

The  same  rule  applies  to  the  fixing  solution.  It  must 
be  fresh  and  clean  to  give  good  results. 

Under  proper  tube  and  current  conditions,  and  with 
correct  length  of  exposure,  a  plate  or  film  should  require 
about  five  minutes  for  its  development. 

To  get  the  most  out  of  a  plate,  it  should  be  developed 
until  fairly  dense,  that  is,  until  it  is  about  the  same  color 
on  each  side.  If,  after  it  has  cleared  in  the  fixing  bath, 
it  appears  too  dark  or  dense,  you  know  that  it  has  been 
overexposed.  Therefore,  in  making  subsequent  expo- 
sures of  similar  patients  and  structures  decrease  the 


DEVELOPMENT    OF    PLATES    AND    FILMS  131 

length  of  exposure.  If,  upon  clearing,  the  image  on  the 
plate  is  faint  and  indistinct,  you  have  reason  to  think  it 
has  been  underexposed.  Therefore,  in  subsequent  ex- 
posures of  similar  cases  increase  the  length  of  exposure. 
Plates  or  films  which  as  the  result  of  overexposure  are 
too  dark  or  dense  for  diagnostic  purposes  may  be  greatly 
improved  by  the  use  of  "a  reducing  solution."  Where 
the  reducing  process  is  to  be  employed  the  fixing  bath 
solution  should  be  removed  from  the  plate  or  films  by 
placing  it  in  running  water  for  several  minutes.  The 
reducing  solution  is  then  prepared  as  follows : 

Solution  A : 

Distilled  Water  1  quart 

Potassium  Ferricianide  1  oz. 

Solution  B: 

Distilled  Water  1  quart 

Hypo  Crystals  1  oz. 

Use  equal  parts  of  Solution  A  and  Solution  B. 

A  sufficient  amount  of  solution  is  placed  in  a  tray  to 
cover  the  plate  or  film  and  the  process  carefully  watched 
until  the  desired  density  is  obtained.  It  is  unnecessary 
to  carry  out  the  process  in  the  dark  room  as  ordinary 
light  does  not  hamper  the  reduction.  When  brought  to 
the  proper  density  the  plate  or  film  should  be  placed  in 
nmning  water  for  about  thirty  minutes. 

AVliile  the  reducing  process  can  often  times  be  em- 
ployed to  advantage  it  is  safe  to  say  that  plates  and 
films  so  treated  are  not  as  highly  satisfactory  as  those 
which  are  correctly  exposed  and  correctly  developed  and 
therefore  need  no  such  treatment. 

Sometimes  after  development  plates  and  films  appear 
very  thin  and  lacking  in  contrast.  If  this  is  the  result  of 
underdevelopment  or  the  use  of  a  weak  or  stale  develop- 


132  DENTAL   AND   ORAL   RADIOGRAPHY 

ing  solution  their  usefulness  can  be  increased  by  the  use 
of  an  intensifying  solution. 
Such  a  solution  may  be  made  as  follows : 

Solution  A : 


Distilled  water 

16  oz. 

Bichloride  of  Mercury 

120  grs 

Potassium  Bromide 

120  grs 

Solution  B : 

Distilled  water 

16  oz. 

Sodium  Sulphite  (dry) 

2  oz. 

The  plate  or  film  to  be  intensified  is  first  well  washed 
so  that  all  the  fixing  bath  solution  is  removed  from  it. 
It  is  then  immersed  in  a  suitable  amount  of  solution  A 
where  it  is  allowed  to  remain  until  it  becomes  thoroughly 
bleached.  When  this  has  been  accomplished  it  is  well 
washed  with  water  and  placed  in  solution  B,  a  sufficient 
amount  being  used  to  cover  it  well.  This  will  cause  it 
to  become  cleared  and  darkened  after  which  it  is  thor- 
oughly washed  in  cold  running  water,  the  entire  process 
being  permissible  outside  of  the  dark  room. 

The  intensifying  process  is  most  useful  where  the  pa- 
tient is  not  available  for  additional  exposures,  but  plates 
and  films  so  treated  cannot  be  regarded  as  being  on  a  par 
with  those  where  all  the  factors  of  correct  exposure  and 
development  have  been  observed  and  therefore  it  should 
be  regarded  in  the  light  of  an  emergency  proceeding. 

By  keeping  the  tube  and  current  conditions  right,  the 
approximate  length  of  exposure  for  any  given  case  is 
usually  easily  determined  by  the  operator,  after  a  little 
experience.  As  stated  before,  this  will  depend  upon  the 
type  of  x-ray  apparatus  used,  the  thickness  and  density 
of  the  parts  to  be  radiographed,  and  the  age  and  struc- 
tural make  up  of  the  patient. 


CHAPTER  X 

THE  INTERPRETATION  OF  DENTAL  AND 
ORAL  RADIOGRAMS 

The  ability  to  correctly  interpret  dental  and  oral  ra- 
diograms is  an  accomplishment  which  every  dentist 
should  possess.  In  fact,  it  should  be  viewed,  not  only  in 
the  light  of  an  accomplishment,  but  as  a  requisite  of 
modern  dentistry. 

Unfortunately,  the  assertion  is  not  infrequently  made 
by  certain  ill-informed  members  of  the  dental  profession 
that  only  minor  importance  should  be  attached  to  the 
findings  of  the  radiogram,  their  claim  being  that  such 
images  can  be  construed  as  showing  conditions  which  do 
not  actually  exist. 

Such  an  attitude  can  be  explained  as  being  the  out- 
growth of  several  things,  among  which  a  lack  of  knowl- 
edge of  the  fundamental  principles  of  radiography  and 
its  various  branches,  and  especially  of  the  science  of  in- 
terpretation, stands  as  an  important  factor.  Therefore, 
opinions  of  the  x-ray  and  its  application  in  dentistry  ex- 
pressed by  those  unqualified,  should  not  be  regarded 
seriously. 

The  idea  also  seems  to  prevail  among  many  poorly  in- 
formed members  of  the  dental  profession  as  well  as 
among  medical  men  of  the  same  type  that  the  interpreta- 
tion of  dental  and  oral  radiograms  is  an  extremely 
simple  matter,  requiring  little  if  any  preparation  on  the 
part  of  the  one  who  is  to  make  the  interpretation.  This 
erroneous  idea  is  doubtless  responsible  for  many  errors 
being  committed  which  naturally  has  the  tendency  to  put 
this   work  in   disrepute.    Without  doubt,   many   useful 

133 


134  DENTAL   AND   ORAL   RADIOGRAPHY 

teeth  have  been  needlessly  sacrificed  through  sheer  in- 
competence on  the  part  of  some  diagnosticians.  Hence, 
the  importance  of  careful  study  and  judgment  in  this 
particular  phase  of  our  work. 

The  first  requisite  of  interpretation  is  an  accurate 
knoivledge  of  the  anatomy  and  physiology  of  the  struc- 
tures involved,  for  a  radiogram  is  a  shadoiv  picture,  and 
a  shadoiv  picture  is  meaningless  unless  one  is  thoroughly 
familiar  ivith  the  main  characteristics  of  the  original. 
The  radiogram  may  be  said  to  vary  from  an  ordinary 
shadow  picture,  as,  in  addition  to  mere  outlines,  varying 
densities  are  shown  due  to  the  fact  that  the  x-ray  pene- 
trates all  matter  in  inverse  ratio  to  its  mass  or  density. 

If  one  is  possessed  of  an  accurate  knowledge  of  the 
anatomy  and  physiology  of  the  dental  and  oral  struc- 
tures, the  next  step  toward  acquiring  the  ability  to  cor- 
rectly interpret  radiograms  of  these  structures,  would 
be  to  become  familiar  with  their  radiographic  appear- 
ance under  normal  conditions,  for  unless  one  be  familiar 
with  the  appearance  in  the  radiogram  of  the  structures 
under  normal  conditions,  it  is  obviously  impossible  to  in- 
telligently recognize  pathologic  or  anomalous  conditions 
unless  they  be  of  a  glaring  nature.  AVlien  we  speak  of 
the  radiographic  appearance  of  the  structures  under 
normal  conditions,  we  refer,  not  only  to  a  freedom  from 
pathologic  or  anomalous  involvement,  but  also  to  the 
character  of  the  radiogram  itself,  which  must  be  normal 
in  that  it  must  he  made  in  accordance  with  a  technic 
which  results  in  the  shadows  of  the  structures  under 
scrutiny  being  imposed  upon  the  plate  or  film  in  their 
correct  proportions. 

Therefore,  it  is  essential  that  in  addition  to  the  before 
mentioned  requisites,  one  ivho  ivould  intelligently  inter- 
pret radiograms  must  understand  enough  of  the  funda- 
mental   rides    of    radiographic    technic    to    knoiv   when 


IjStteepretatiox  of  radiograms  135 

examining  a  radiogram,  whether  or  not  the  technic  in- 
volved in  its  making  was  correct  or  faidty,  and  if  faidty, 
whether  or  not  the  degree  of  fault  is  sufficient  to  render 
it  so  inaccurate  as  to  he  useless. 

In  correctly  made  radiograms,  the  dental  and  oral 
structures  under  normal  conditions  have  a  characteristic 
appearance,  for,  owing  to  the  varying  densities  of  the 
contained  structures  in  our  field,  they  appear  upon  the 
plate  or  film  in  a  manner  most  advantageous  for  obser- 
vation. For  instance,  it  will  be  noted  upon  the  examina- 
tion of  such  a  radiogram,  that  metallic  fillings,  if  they 
are  present,  appear  as  white  masses,  and  root  fillings  as 
somewhat  less  dense  lines.  The  enamel  and  dentin  are 
next  in  density,  while  root  canals  show  plainly  as  dark 
channels  in  the  dentin,  and  the.  alveolar  process  and  max- 
illae show  their  fine  uniform  cancellous  structures  in  vari- 
ous degrees  of  density,  depending  upon  their  thickness. 

In  examining  a  radiogram,  it  is  essential  that  the 
original  plate  or  film  only  be  used,  and  this  should  be 
examined  carefully  and  in  a  proper  light,  if  the  maximum 
amount  of  information  is  to  be  obtained  from  it. 

This  is  best  accomplished  by  utilizing  some  sort  of 
illuminating  box  or  cabinet  from  which  varied  degrees 
of  light  are  obtainable.  The  face  of  such  a  cabinet 
should  be  covered  with  ground  glass,  so  that  the  light 
transmitted  will  be  equally  distributed  and  free  from 
shadows.  As  a  radiogram  is  a  transparency^,  a  dim  light 
behind  it  will  bring  out  one  set  of  shadows  to  their 
greatest  clearness.  An  increase  in  the  light  will  show 
forth  still  other  effects ;  while  a  high  degree  of  illumina- 
tion will  bring  out  the  more  dense  portions. 

In  this  manner  each  portion  of  the  radiogram  may  be 
studied  under  a  degree  of  light  destined  to  bring  out  the 
maximum  amount  of  detail. 

Now  with  a  "print"  or  "lantern  slide"  one  can  study 


136  DENTAL   AND   ORAL   RADIOGRAPHY 

the  field  only  from  a  one  light  aspect  and  oftentimes  in 
order  to  secure  any  detail  in  the  higher  or  less  dense 
areas,  it  will  be  found  that  the  dense  areas  must  be 
printed  almost  to  an  inky  blackness.  This  fact  accounts 
for  the  unsatisfactory  appearance  of  many  radiograms 
used  as  illustrations  in  our  journals  and  text  books,  for 
when  reduced  to  halftone  engravings,  mucli  of  their  val- 
uable detail  is  lost. 

In  examining  intra-oral  radiograms,  it  is  an  advan- 
tage to  place  them  in  a  film  mount  which  will  hold  them 
securely  and  render  it  unnecessary  to  view  them  while 
being  held  between  the  fingers.  Such  a  ''mount"  should 
preferably  be  made  of  celluloid  with  one  side  clear  and 
the  other  side  dull,  which  allows  the  light  transmitted 
to  be  of  the  same  character  as  that  coming  through 
ground  glass. 

If  one  be  unfamiliar  with  the  fundamental  rules  of  ra- 
diographic technic,  he  cannot  know,  when  examining  a 
radiogram,  just  what  portions  of  it  are  to  be  relied  upon 
to  give  dependable  information,  for  as  a  rule,  owing  to 
anatomic  arrangement  of  the  structures  in  our  field,  only 
limited  areas  can  be  relied  upon  to  be  "in  focus"  in  each 
radiogram.  But  if  one  is  possessed  of  an  accurate 
knowledge  of  the  anatomy  and  physiology  of  the  parts 
involved,  understands  the  fundamental  rules  of  radio- 
graphic technic,  and  is  familiar  with  the  appearance  in 
the  radiogram  of  the  dental  and  oral  structures  under 
normal  conditions,  it  should  by  no  means  he  difficult  to 
see  any  alterations  or  changes  ivhich  occur  in  these  struc- 
tures as  a  result  of  anomalous  or  pathologic  conditions. 

The  mere  ability  to  note  an  alteration,  or  change,  in 
the  structures  does  not  fulfill  the  requirements  of  intelli- 
gent interpretation,  for  these  alterations,  or  changes, 
can  have  their  full  significance  only  to  one  tvho  under- 
stands the  pathologic  conditions  ivhich  may  develop  in 


INTEKPEETATIOlSr    OF    RADIOGRAMS  137 

these  structures,  and  the  character  of  the  anatomic 
changes  which  they  bring  about.  Therefore,  it  should 
be  apparent  that  the  ability  to  intelligently  interpret  ra- 
diograms is  not  a  thing  to  be  acquired  overnight,  but 
must  come  as  the  result  of  study  in  several  important 
branches,  and  anyone  who  attempts  it  otherwise  as- 
sumes responsibilities  unworthily. 

The  essential  requirements  of  radiograms  to  be  used 
as  an  aid  in  diagnosis  may  be  briefly  considered  under 
two  classes.  In  the  first,  we  may  place  those  which  may 
be  useful  in  determining  the  presence  or  absence  of 
grosser  lesions  or  anomalies,  such  as  fractures  of  the 
maxillae,  impacted  or  unerupted  teeth,  large  cysts  or 
tumors,  the  presence  of  foreign  bodies,  etc.  In  the  sec- 
ond class,  would  be  included  individual  teeth  and  their 
investing  tissues,  the  peridental  membrane  and  alveolar 
bone.  Both  of  these  classes  are  important  and  essential 
if  the  x-ray  is  to  render  the  maximum  service.  In  either 
instance,  a  standardised  and  exact  technic  are  essential. 

In  the  first  class  mentioned,  viz.,  the  grosser  lesions  or 
anomalies,  extra-oral  radiograms  frequentl}'^  prove 
highly  advantageous  for  they  render  accessible  areas 
and  structures,  the  images  of  which  may  not  always  be 
satisfactorily  impressed  upon  the  smaller  films.  The 
diagnostician  should  therefore  familiarize  himself  with 
the  appearance  of  the  structures  as  they  appear  in  such 
radiograms  under  normal  conditions  for,  owing  to  the 
fact  of  the  difference  of  technic  required,  greater  dis- 
tances of  penetration  of  the  rays,  with  the  resultant  dif- 
fering appearance  of  the  finished  product  when  com- 
pared to  intra-oral  radiograms,  some  confusion  may 
occur.  However,  when  one  is  really  familiar  with  the  ap- 
pearance of  the  grosser  structures  in  such  radiograms 
under  normal  conditions,  the  anomalous  and  pathological 
is  not  difficult  to  discern. 


138  DENTAL   AND    ORAL   RADIOGRAPHY 

In  the  second  class,  viz.,  where  individual  teeth  or 
groups  of  teeth  with  their  investing  tissues  are  under 
examination,  it  is  extremely  important  that  not  only  the 
tooth  (or  teeth)  be  reproduced  in  the  film,  but  that  the 
peridental  membrane  and  alveolar  hone  surrotmding  the 
roots,  both  marginally  and  apically  he  shoivn  to  the  best 
advantage.  When  such  a  result  is  not  accomplished,  the 
radiogram  cannot  be  considered  a  safe  or  suitable  diag- 
nostic aid. 

One  error  which  frequently  proves  a  stumbling  block 
for  the  young  diagnostician  is  due  to  the  fact  that  cer- 
tain types  of  lesions  are  supposed  to  have  a  more  or  less 
stereotyped  appearance  in  radiograms  and  while  this 
may  be  true  of  some  of  the  grosser  conditions,  it  still  re- 
mains a  fact  that  really  dangerous  and  unhealthy  condi- 
tions may  exist  which  do  not  manifest  themselves  in  any 
marked  manner.  In  other  words,  it  is  essential  that  the 
most  even  degree  of  detail  possible  shall  be  obtained  and 
that  in  the  examination  of  the  finished  radiograms,  care- 
ful study  of  them  shall  be  made.  This  does  not  mean 
merely  illuminating  the  radiogram  for  an  instant  but 
it  means  the  carefid  study  of  it  under  light  conditions 
favoring  the  maximum  detail. 

The  normal  alveolar  process  when  correctly  radio- 
graphed has  a  distinct  appearance  owing  to  its  anatomi- 
cal structure  and  chemical  composition.  There  is  an 
irregularity  of  the  cancellations  and  a  harmonious 
blending  of  lights  and  darks  in  the  picture.  The  irregu- 
larity of  the  cancellations,  is  due  to  the  fact  that  the 
spaces  which  constitute  spongy  bone  ai:e  irregular  in 
shape  and  size  for  spongy  bone  is  made  up  of  lamellae, 
which  instead  of  being  laid  down  in  an  orderly  manner 
as  in  compact  bone,  are  arranged  in  an  irregular  man- 
ner. These  groups  of  lamellae  form  strands  of  bone  tis- 
sue which  unite,  and  in  uniting,  form  irregular  shaped 


INTERPRETATIOISr    OF    RADIOGRAMS  139 

cavities.  For  this  reason,  a  picture  of  spongy  bone  when 
normal,  shows  white  lines  composed  of  thin  and  delicate 
strands  of  bone  tissue  enclosing  dark  areas,  no  two  of 
which  are  exactly  alike.  So  it  may  be  definitely  stated 
that  the  appearance  of  the  normal  alveolar  process  pre- 
sents an  appearance  of  irregularly  shaped  minute  cavities 
surrounded  by  fine  delicate  white  strands  of  bone  struc- 
ture.    (Fig.  61.) 

It  is  a  demonstrated  fact  that  when  the  bone  is  sub- 
jected to  injurious  influences,  the  cancellations  lose  their 
clear-cut  borders  and  become  smaller  and  closer  together. 
Therefore,  whenever  cancellated  structure  tends  to  be- 
come regular,  ill-defined  and  homogeneous,  the  suspicion 
of  pathological  processes  is  entirely  justified. 

As  the  presence  of  calcium  salts  in  the  bone  tends  to 
obstruct  the  passage  of  the  rays,  any  increase  or  de- 
crease of  this  factor  will  become  apparent  upon  the  sensi- 
tive photographic  emulsion,  an  increase  being  visible  as 
an  area  of  greater  density,  (a  lighter  area)  while  a  de- 
crease of  this  element  shows  a  lessened  density  or  darker 
area.  These  radiographic  changes  are  spoken  of  in  the 
former  instance  as  radiopaque  areas  and  in  the  latter  in- 
stance as  radioluceut  areas,  terms  which  are  quite  de- 
scriptive and  have  found  a  permanent  place  in  our 
nomenclature. 

In  the  study  of  radiograms  therefore,  a  definite  effort 
should  be  put  forth  to  detennine  whether  or  not  varia- 
tions from  the  normal  have  occurred,  and  if  it  can  be 
definitely  demonstrated  that  such  is  the  case,  the  next 
problem  is  to  determine  ichy  such  changes  should  have 
occurred.  While  in  numerous  instances,  the  cause  may 
be  apparent  in  the  radiogram,  many  others  may  be  en- 


140 


DENTAL   AND   ORAL   RADIOGRAPHY 


conntered  where  the  cause  is  obscure  or  subject  to  ques- 
tion.   This  brings  the  diagnostician  face  to  face  with  an 


Fig.    61-/4. — Intra-oral    radiograms    of    groups    of    teeth    and    adjacent    tissues    under 

normal   conditions. 


important  factor  very  frequently  overlooked,  viz.,   the 
clinical  findings.    Kegardless  of  the  value  we  place  upon 


IJSTTERPRETATIOiSr    OF    EADIOGRAMS 


141 


the  x-ray,  we  should  never  commit  the  error  of  failing 
to  take  into  full  consideration  all  circumstances  connected 


Fig.    Ol-B. — Intra-oral    radiograms    of    groups    of    teeth    and    adjacent    tissues    under 

normal  conditions. 


with  the  case  under  examination,  including  its  history, 
conditions  of  dentition  and  occlusion,  as  well  as  the  physi- 
cal state  of  the  soft  tissues  of  the  mouth. 


142 


DENTAL   AND    ORAL   RADIOGRAPHY 


Unfortunately,  this  has  not  always  been  done,  or  at 
least  it  has  not  been  universally  practised  during  that 
hysterical  era  just  passed  during  which  so  many  pulp- 
less  teeth  have  been  needlessly  slaughtered.    Fortunately 


I 


Fig.  62. — Instances  where  inflammatory  processes  have  resulted  in  a  hypertrophy 
of  the  peridental  membrane  and  resultant  encroachment  ujjon  the  alveolar  bony 
structures.  In  the  instances  shown,  the  clinical  findings  gave  confirmation  of  the 
fact   that   these   were   chronic   dento-alveolar   abscesses. 


INTERPRETATION    OF    RADIOGRAMS 


143 


for  our  patients  we  are  now  entering  upon  a  period  of 
greater  conservatism  as  a  result  of  past  experience  and 
a  more  accurate  knowledge  of  the  subject  which  this  ex- 
perience has  brought. 

One  eminent  investigator*  in  this  field  has  demon- 
strated a  very  important  fact  in  regard  to  radiographic 
variations  which  the  student  should  bear  in  mind,  viz., 
that  infection  is  not  the  only  cause  for  radiographic  vari- 
ations in  films  and  that  infection  and  inflammation  are 
not  necessarily  synonymous.    In  radiographic  variations, 


Fig.     63. — Chronic    tiento-alveolar     abscesses    with    cystic     formation. 

such  factors  as  hyperocclusion,  disuse,  chemical  influ- 
ences and  pressure  are  likewise  influences  which  must 
be  considered  possibilities  in  interpreting  such  changes. 
In  judging  the  relationship  of  individual  teeth  to  any 
suspected  condition,  two  structures  having  a  character- 
istic radiographic  appearance  should  be  carefully  scru- 
tinized.   These  are  the  peridental  membrane,  showing  as 


1922. 


*Dr.   Joseph    Pollia.      The   Journal    of   the    National    Dental    Association,    January, 


144 


DENTAL   AND   ORAL   RADIOGRAPHY 


a  fine  block  line,  and  the  peridental  lamella,*  visible  as  a 
fine  tvhite  line  A    The  characteristic  appearance  of  these 


Fig.    64. — Three    instances   of    true    cysts    occurring   in    the    mandible. 

two  structures  is  due  in  the  former  instance  to  the  fact 
that  the  soft  tissue  of  the  membrane  offers  little  resist- 


II 


*Terms    suggested    by    Dt.    Joseph    Pollia   to    be    used    instead    of    cribriform    plate. 

tThe  white  line  of  demarcation  which  is  intact  around  a  normally  disposed  tooth 
was  first  called  to  the  attention  of  the  profession  by  Dr.  Iceland  Carter.  (Interna- 
tional  Journal    of    Orthodontia,    July,    1917.) 


liSTTEEPRETATION    OF    RADIOGRAMS 


145 


ance  to  passage  of  the  rays  and  therefore  throws  no 
radiopaque  impression,  while  in  the  latter  instance,  the 
thin  compact  bone  resists  the  passage  of  the  rays  and  is 
visible  as  a  thin  radiopaque  line.  About  a  healthy  tooth, 
these  tifo  structiires  shoiv  no  variation  of  thickness  or 
contour. 

If  a  pathological  process  has  its  origin  from  within  a 
tooth,  the  first  structure  to  be  subjected  to  its  influence 


Fig.   65. — Radiolucent   areas   adjacent   to   the   roots   of    teeth   which    are   characteristic 
of  necrosis   or  rarefying  osteitis. 

is  the  peridental  membrane  which  naturally  makes  it 
the  first  structure  to  show  abnormality.  This  is  indi- 
cated by  a  thickening  of  the  fine  black  line  at  the  point  of 
irritation.  As  the  membrane  is  closely  encased  by  the 
peridental  lamella,  its  thickening  or  hypertrophy  pushes 
out  the  peridental  lamella,  causing  it  to  sag  or  lose  its 
normal  contour  at  the  seat  of  the  inflammatory  process. 
If  the  inflammatory  process  is  unchecked  and  continues 


146 


DENTAL   AND   ORAL   RADIOGRAPHY 


to  progress,  the  hypertrophy  of  the  peridental  membrane 
continues  with  a  resultant  encroachment  upon  the  alveo- 
lar bony  structures.     (See  Fig.  62.) 

With  the  changes  in  nutrition  which  accompany  pro- 
gressive inflanmiatory  processes,  there  is  a  resultant  de- 
crease of  calcium  salts  in  the  adjacent  alveolar  bone  as 


I 


Fig.   66. — Radiopaque  areas  about  the   roots  of  teeth  or  in  the  alveolar  bone  indicating 
defensive   bone   reaction. 


well  as  a  diminution  of  the  bone  units  or  lamellae  which 
lessens  the  resistance  usually  offered  by  these  structures 
to  the  passage  of  the  rays.  For  this  reason,  the  photo- 
graphic emulsion  is  more  readily  affected  and  the  area 
is  rendered  more  radiolucent  than  is  characteristic  of 
normal  structure.     While  the  changes  described  above 


INTERPEETATION    OF    EADIOGRAMS 


147 


are  perhaps  more  frequently  due  to  infection  than  to 
other  causes,  it  is  possible  for  them  to  be  the  result  of 
other  conditions  such  as  trauma  or  hyperocclusion,  pres- 


"♦^iJTiJ 


#bj 


Fig.    67. — Characteristic   appearance   of  the   investing   tissues    in   well    developed    pyor- 
rhea alveolaris. 

sure,  or  chemical  influences  so  that  all  clinical  facts 
should  be  carefully  weighed  before  coming  to  a  definite 
conclusion. 


148  DENTAL   AND   ORAL   RADIOGRAPHY 

Cysts  and  tumors  of  the  maxillae,  owing  to  the  char- 
acter of  tissue  changes  which  characterize  their  develop- 
ment are  visible  radiographically  as  radiolucent  areas. 
Differentiation  of  the  character  of  the  lesion  however  is 
not  to  be  judged  by  this  feature  alone  but  more  by  the 
extent  of  the  area  affected  and  the  clinical  findings. 
(Fig.  63.) 

It  will  be  recalled  that  the  true  cyst  differs  from  the 
cystic  formation  frequently  accompanying  chronic  dento- 
alveolar  abscesses  in  that  it  has  an  epithelial  lining  w^hich 
definitely  limits  its  extent  although  it  usually  attains 
considerable  size,  depending  upon  its  character  and 
cause.  On  the  other  hand,  cystic  formation  accompany- 
ing chronic  dento-alveolar  abscesses  are  usually  less  ex- 
tensive as  they  result  from  the  necrosis  and  liquefaction 
of  the  central  portion  of  the  inflammatory  process  due 
to  lack  of  nutrition.  In  either  event,  such  lesions  are 
radiographically  demonstrated  as  radiolucent  areas,  but 
their  definite  character  must,  as  has  already  been  em- 
phasized, be  determined  by  their  size  and  by  such  other 
clinical  signs  as  may  be  indicative  of  their  true  character. 
(Figures  63  and  64.) 

Necrosis,  Rarefying  Osteitis,  or  Caries  within  the  al- 
veolar bone  or  its  supporting  structures  are  manifest  in 
the  radiogram  as  radiolucent  areas  but  differ  in  appear- 
ance from  cysts  or  dento-alveolar  abscesses  in  that  there 
is  a  less  distinct  line  of  demarcation  between  the  radio- 
lucent area  and  the  surrounding  tissue.  In  such  in- 
stances, the  borders  of  the  radiolucent  area  show  a  grad- 
ual increased  radiopacity  until  normal  tissue  is  shown. 
This  fact  is  easily  understood  when  we  recall  the  pro-  | 
gressive  character  of  these  lesions  and  the  character  of  [- 
tissue  changes  which  accompany  them. 

Thus  far  only  those  conditions  which  might  be  termed 
progressive  inflannnatory  processes  and  which  are  ap- 
parent   as     radiolucent    areas    have    been    discussed. 


INTERPRETATION    OF    RADIOGRAMS 


149 


Another  type  of  radiographic  variation  sometimes  en- 
countered and  which  is  apparent  as  an  area  of  increased 
radiopacity  is  important.  In  such  instances  the  reaction 
of  the  alveolar  bone  may  be  defensive  in  character  re- 
sulting in  an  increase  in  the  number  of  bone  units  and 
hence  to  an  increased  resistance  to  the  passage  of  the 


Fig.    68. — A  cuspid   tooth   lying  against   the   anterior   v/all   of  the   antrum. 

rays.  In  this  defensive  process  there  is  an  increased 
deposition  of  lamellae  which  in  some  instances  may  ren- 
der the  bone  structure  in  the  area  affected  very  dense 
and  compact  in  character.  This  condition  which  is 
doubtless  due  to  a  morbid  increase  of  nutrition  may  as 
in  the  case  of  the  progressive  inflammations  be  due  to 
infection,  trauma  or  hyperocclusion,  thermal  shock,  de- 


150 


DENTAL   AND   ORAL   RADIOGRAPHY 


fensive  reaction,  or  to  such  unknown  influences  as  may 
produce  such  bone  changes.  In  any  event,  such  condi- 
tions when  demonstrated  require  no  small  degree  of 
study  and  judgment  in  correctly  accounting  for  their 
existence.    (Fig.  66.) 

Either  of  the  above  mentioned  types  of  radiographic 
variations  (i.  e.,  the  progressive  or  defensive)  may  be 
encountered  in  alveolar  bone  even  after  all  the  teeth  have 
been  removed  especially  so  if  one  or  more  of  the  roots  of 


1 


Fig.  69. — A  radiogram  to  determine  the  state  of  dentition  of  the  right  side  in 
the  mouth  of  a  child  eleven  years  old.  The  developing  second  molars  pre  shown, 
likevi^ise  the  upper  second  bicuspid  and  the  lower  first  bicuspid  about  to  erupt.  It 
will  be  noted  that  the  lower  second  deciduous  molar  has  no  successor,  nor  is 
there  an   upper  first   bicuspid   present  in   the  jaw. 


teeth  previously  held  had  been  the  source  of  an  infectious 
process.  If  upon  the  removal  of  such  teeth,  the  infected 
area  is  not  eliminated  either  through  natural  means  or 
through  curettement,  the  condition  may  persist  and  if 
such  is  the  case,  may  be  demonstrated  by  properly  made 
radiograms. 


INTERPRETATIOlSr    OF    RADIOGRAMS 


151 


Where  a  destructive  process  has  ensued  in  the  peri- 
dental membrane,  or  in  the  bony  wall  of  the  alveolus 
(pyorrhea  pockets),  the  extent  of  the  changes  occurring 
may  be  quite  definitely  determined  through  a  study  of  the 
structures  first  affected,  viz.,  the  peridental  membrane 
(the  fine  black  line)  and  the  peridental  lamella  (the  fine 
white  line).  In  such  instances,  the  progress  of  the  lesion 
extends  from  the  margin  of  the  alveolus  in  an  apical  di- 
rection, hence  its  extent  is  not  difficult  to  determine  es- 
pecially if  occurring  upon  the  mesial  or  distal  side  of  the 
tooth.     (Fig.  67.) 

Visualizing  the  grosser  lesions  should  offer  little  dififi- 


Fig.   70. 


Fig.    71-A. 


Fig.    70. — Root   canal   fillings   in   a   lower   first    molar. 

Fig.    7\-A. — Root   canal    filling   material    forced   beyond    the   root   apex    of    an    upper 
second  bicusoid. 


culty  for  as  a  tooth  is  much  more  dense  than  the  bony 
structures  of  the  jaw  or  adjacent  parts,  any  anomaly  of 
form,  size  or  position  is  easily  discernible  even  though  it 
occupy  a  position  far  from  what  might  be  expected,  as 
for  instance,  in  the  case  of  impacted  molars,  teeth  m 
the  antrum,  etc.  (See  Figure  68.)  Likewise,  and  for  the 
same  reason,  the  presence  in  or  absence  from  the  jaws 
of  successors  of  the  deciduous  teeth  can  easily  be  deter- 
mined, as  well  as  the  state  of  development  of  any  un- 
erupted  tooth.    (Fig.  69.) 

Fractured  roots  or  fractures  of  the  bone  even  without 


152 


DENTAL   AND   ORAL   RADIOGRAPHY 


displacement  are  often  discernible  at  the  line  of  fracture, 
owing  to  the  fact  that  the  line  of  fracture  offers  less  re- 


Fig.  71-B. — Instances  where  the  roots  of  teeth  lie  in  close  proximity  to  the  antrum 
or  accessory  antral  cells.  Not  infrequently,  serious  errors  of  diagnosis  are  made 
in  such   instances. 


sistance  to  the  penetration  of  the  rays,  and  therefore,  is 
apparent  upon  the  plate  or  film  as  a  dark  line. 


INTERPRETATIOlSr    OF    RADIOGRAMS  153 

The  different  filling  materials  vary  but  little  in  relative 
gradation  of  density,  and  when  used  as  root  filling  mate- 
rials, are  plainly  visible  as  light  lines.  Because  they 
differ  in  density  from  cementum  and  dentin,  the  extent  to 
which  they  have  been  introduced  into  the  root  canals  is 
easily  discernible.  (See  Figs.  70  and  71.)  Broken  off 
broaches  and  other  instruments,  or  small  wires  intro- 
duced into  root  canals  to  determine  their  length  or  the 
extent  to  which  they  have  been  opened,  because  of  their 
great  density,  appear  very  white  and  are  easily  differ- 
entiated from  root  canal  fillings  or  tooth  structure. 

In  the  study  of  radiograms  of  the  alveolar  bone,  and 
their  supporting  bony  structures,  caution  should  be  ex- 
ercised in  the  misinterpretation  of  such  natural  cavities 
as  the  antrii,  nasal  cavities,  or  nerve  openings  or  canals 
such  as  the  mental  foramina,  etc.  Owing  to  their  prox- 
imity to  the  roots  of  the  teeth,  the  error  is  not  infre- 
quently committed  of  confusing  them  with  radiolucent 
areas  of  pathological  significance,  an  error  which  natu- 
rally proves  disastrous  to  patients  if  operative  measures 
are  carried  out. 

In  seeking  out  the  various  anomalies  and  pathologic 
conditions  to  which  the  teeth  and  oral  structures  are 
subject,  ive  sJwuld  not  be  misled  by  indefinite  shadows  in 
radiograms.  The  very  nature  of  these  structures,  their 
gross,  as  well  as  minute  anatomy  renders  them  somewhat 
difficult  to  radiograph,  and  necessitates  a  refinement  of 
technic  greater  than  that  demanded  with  most  of  the 
other  portions  of  the  human  anatomy.  Therefore,  only 
radiograms  made  in  accordance  with  a  definite  and  exact- 
ing technic  should  be  relied  upon  as  diagnostic  aids.  If 
a  doubt  exists  in  any  given  instance,  an  additional  or 
even  several  more  exposures  should  be  made,  so  that  any 
conclusions  reached  ivill  be  founded  upon  definite  evi- 
dence. 


CHAPTER  XI 

INDICATIONS  FOR  THE  USE  OF  THE  X-RAY 
IN  THE  PRACTICE  OF  DENTISTRY 

Prior  to  the  discovery  of  the  x-ray  and  its  adoption  in 
dental  practice,  the  diagnosis  of  many  abnormal  condi- 
tions in  the  alveolar  process  and  in  the  maxilla  or  mandi- 
ble proper  had  to  be  accomplished,  or  at  least  attempted 
by  the  dentist  largely  by  relying  upon  his  ''judgment'^ 
and  *' experience. "  As  these  excellent  attributes  are  not 
infallible,  the  progessive  members  of  the  profession  were 
quick  to  recognize  in  the  x-ray,  a  veritable  godsend,  be- 
cause it  rendered  more  positive  and  accurate  than  here- 
tofore, the  diagnosis  of  many  pathologic  conditions.  It 
has  also  aided  just  as  materially  in  prognosis  and  treat- 
ment. In  fact,  so  indispensable  has  it  become  that  if 
the  dentist  attempts  certain  operations  without  its  aid, 
he  assumes  unworthily  his  professional  responsibilities. 

In  enumerating  the  many  instances  where  this  agent 
should  be  used,  the  author  will  not  attempt  to  give 
preference  or  importance  to  any  particular  tield,  or  to 
classify  the  indications  in  the  order  of  their  frequency 
of  occurrence,  for  this  Avill  depend  largely  upon  the 
character  of  practice  enlisting  the  efforts  of  different 
men.  "VMien  the  need  arises  for  its  use,  it  should  he 
used  whether  the  need  arises  in  the  practice  of  the  or- 
thodontist, prosthedontist,  oral  surgeon,  or  general 
practitioner,  etc.,  for  the  obligation  is  the  same  if  the 
dentist  expects  to  do  his  full  duty  by  his  patients. 

For  Purposes  of  General  Oral  Examination 
Not  infrequently  the  dentist  is  consulted  by  patients 
who  are  undergoing  no  discomfort  or  pain  from  their 

154 


INDICATIONS    FOR   X-RAY    IN    DENTISTRY  155 

teeth,  but  realizing  their  importance  as  etiologic  factors 
of  systemic  disease,  wish  to  undergo  a  thorough  exami- 
nation. In  many  instances,  such  an  examination  will  not 
be  complete  without  a  radiographic  survey  of  the  mouth. 
Especially  is  this  true  where  such  patients  have  pulpless 
teeth,  or  where  large  fillings,  bridge  work  or  crowns 
are  present.  Notwithstanding  the  fact  that  often  the 
clinical  history  of  such  cases  reveals  nothing  that  will 
lead  the  dentist  to  believe  that  active  septic  foci  have 
existed  in  such  mouths,  the  radiographic  examination 
should,  nevertheless,  be  made,  for  in  the  light  of  our 
present  knowledge,  it  must  be  concluded  that  these  con- 
ditions frequently  exist  without  subjective  or  objective 
symptoms. 

Such  examinations  are  particularly  important  in  the 
case  of  patients  suffering  from  some  systemic  conditions, 
who  are  referred  by  a  physician  to  determine  whether  or 
not  the  teeth  are  an  etiologic  factor. 

Where  such  an  examination  reveals  no  active  septic 
foci,  but  shows  the  presence  of  one  or  several  pulpless 
teeth  with  root  canal  fillings  which  do  not  measure  up 
to  the  full  requirements  of  such  fillings,  it  is  important 
that  such  teeth  be  resubjected  to  radiographic  examina- 
tion at  regular  intervals  to  see  whether  or  not  they  re- 
main in  a  healthy  state. 

Radiographic  Requirements. — In  order  to  do  justice 
to  such  cases,  extra-oral  radiograms  should  be  made  of 
each  side.  These  should  show  the  upper  and  lower  teeth 
and  adjacent  structures  posterior  to  the  cuspids.  Intra- 
oral radiograms  of  the  upper  and  lower  incisors  and 
cuspids  should  also  be  secured,  and  the  whole  series  de- 
veloped and  examined.     (See  Fig.  72.) 

Where  the  extra-oral  radiograms  show  suspicious 
areas  about  the  teeth  which  do  not  show  with  sufficient 
clearness  to  meet  the  demands  of  diagnosis,  intra-oral 


156 


DENTAL  AND   ORAL   RADIOGRAPHY 


radiograms  may  then  be  made  of  these  areas,  as  a  means 
of  confirmation.  (See  Fig.  73.)  Some  operators  prefer 
to  nse  the  intra-oral  method  entirely,  in  making  a  general 
examination,  but  this,  in  the  author's  opinion,  is  a  mis- 
take, for  the  reason  that  all  areas  of  pathologic  impor- 
tance are  not  accessible  to  these  small  films. 


Fig.  72. — Extra-oral  radiogram  of  the  right  side  made  for  purposes  of  general  ex- 
amination. Suspicious  areas  are  to  be  seen  above  the  upper  first  bicuspid  and  about 
roots  of  the  lower  second  molar.     An   unerupted  upper  third   molar  is  also  visible. 


To  Determine  the  Seat  of  Pericemental  Infections 

Not  infrequently  it  is  a  difficult  matter  to  determine 
the  tooth  responsible  for  a  pericemental  infection  or  an 
alveolar  abscess,  as  the  inflammatory  process  may  be  in 
progress  in  the  region  of  several  teeth,  each  of  which 
may  be  under  suspicion,  or  the  infected  area  may  be  at 
a  point  remote  from  the  suspected  tooth.  A  radio- 
graphic examination  will  quickly  settle  all  doubts,  for  the 
radiogram  will  reveal  the  source  and  determine  whether 


INDICATIONS   FOR   X-RAY   IN   DENTISTRY 


157 


or  not  one  or  more  teeth  are  involved.  It  will  likewise 
show  the  extent  to  which  the  periapical  tissues  have  be- 
come involved  and  will  often  shed  valuable  information 
on  the  prognosis  of  the  case.     (See  Figs.  73,  74  and  75.) 


Fig,  73. 


Fis.  74. 


Fig.  7i. — Intra-oral  radiogram  used  as  a  means  of  confirmation  of  the  findings  of 
the  extra-oral   radiogram. 

Fig.  74. — Alveolar  abscesses  are  shown  to  be  present  at  the  apex  of  each  bicuspid 
root. 


Fig.  75. 


Fig.  76. 


Fig.    75. — Upper   bicuspid   teeth   with   abscesses. 

Fig.    76. — Severe   inflammatory   process  in   progress   about   an    uj/per   lateral   incisor. 
The  root  end  shows  a   marked   hypercementcsis.    ■ 


Radiographic  Requirements. — ^Intra-oral  radiograms 
will  usually  suffice.  Where  the  lower  molars  and  bicus- 
pids are  under  examination,  and  the  tissues  under  the 
tongue  are  very  tender,  the  extra-oral  method  can  be  used 
to  advantage,  if  the  patient's  comfort  is  a  consideration. 
(See  Fig.  77.) 


158  DENTAL   AND   ORAL   RADIOGRAPHY 

Root  Canal  Treatment 

Of  the  various  dental  operations,  there  is  none  that  is 
more  universally  in  need  of  further  elucidation  than  the 
treatment  and  filling  of  root  canals.  As  generally  prac- 
ticed at  the  present  time,  this  work  can  easily  be  termed 
the  ''greatest  shortcoming  of  dentistry."  To  those  who 
lecognize  the  uncertainty  of  results  in  this  field,  and  the 
serious  results  which  accompany  failure  to  render  sterile 


Fig.   n. — Extra-oral   radiogram    of   the   lower  molars   showing   the   presence   of   a   large 
dento-alveolar   abscess. 

and  to  completely  fill  root  canals,  the  x-ray  offers  indis- 
pensable aid. 

Before  considering  the  treatment  of  a  tooth  (or  teeth), 
a  radiogram  should  be  made  to  show  the  topography  of 
the  roots  to  be  treated.  If  these  are  proved  to  be  ana- 
tomically within  the  range  of  treatment,  an  attempt  may 
then  be  made  to  remove  all  organic  material  from  the 
canals  and  to  open  them  up  to  the  very  apical  foramen. 
Fine  diagnostic  wires  should  then  be  inserted  and  car- 
ried to  the  end  of  the  canal,  or  as  far  as  the  operator  has 


INDICATIOlSrS    FOR   X-RAY    IN   DENTISTRY 


159 


been  able  to  introduce  the  broaches.  After  sealing  them 
in  with  gutta  percha,  a  second  radiogram  should  be 
made.  Because  of  their  greater  density,  the  wires  will 
show  distinctly  in  the  radiogram  and  will  enable  the 
operator  to  determine  to  what  extent  the  canal  or  canals 
have  been  opened.  It  will  likewise  determine  whether 
any  opening  leading  from  the  pulp  chamber  is  a  canal  or 
a  perforation. 


A. 


C. 

Fig.  78. — A,  two  upper  bicuspid  teeth  with  impeirfectly  filled  canals;  B,  the  same 
teeth  with  the  canals  cleaned  out  and  diagnostic  wires  in  place;  C,  the  same  teeth 
after  the   root  canals  have  been  filled. 

When  the  canals  are  open  to  the  end  (as  shown  by 
the  inserted  wires)  and  the  necessary  treatment  and 
sterilization  has  been  completed,  the  root  canal  fillings 
can  then  be  inserted.  Another  radiogram  should  then 
be  made  to  determine  whether  or  not  the  root  fillings  ex- 
tend to  the  apical  foramina  and  seal  the  canals.  If  they 
do  not,  they  should  be  removed  and  the  before-men- 


160 


DENTAL   AND   ORAL   RADIOGRAPHY 


B. 


Fig.  79. — A,  lower  second  bicuspid  needing  root  canal  treatment  and  filling;  B, 
same  tooth  with  canal  cleaned  out  and  diagnostic  wire  in  place;  C,  same  tooth  with 
the  root   canal   filled. 


Fig.  80. — A,  an  upper  first  bicuspid  needing  root  canal  treatment  and  filling;  B,  canals 
have  been  cleaned  out  and  diagnostic  wires  put  in  place;   C,  canals  filled. 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY 


161 


tioned  operative  and  roentgenographic  process  repeated 
until  success  is  obtained. 

Even  when  all  precautions  are  taken  and  results  seem 
eminently  satisfactory,  several  radiograms  should  be 
made  at  regular  intervals  of  from  three  to  six  months 
following  the  filling  of  the  roots,  to  determine  whether 
or  not  the  operation  has  been  successful,  so  far  as  the 
periapical  tissues  are  concerned.    This  is  especially  im- 


c.  D. 

Fig.   81. — A,  showing  condition   present;  B,   diagnostic   wires  inserted;    C,   root   canals 
filled;   D,   resection  of  roots. 


portant  where  roots  have  been  the  seat  of  periapical  in- 
fections prior  to  the  time  when  treatment  was  inaugu- 
rated.    (See  P^igs.  78,  79  and  80.) 

Radiographic  Requirements. — Intra-oral  radiograms 
exclusively  should  be  used  for  this  work.  An  excep- 
tion might  be  made  in  the  case  of  the  lower  molars  and 
bicuspids,  if  the  tissues  under  the  tongue  are  sufficiently 


162 


DENTAL   AND   ORAL   RADIOGRAPHY 


tender  to  make  the  placing  of  the  films  for  exposure  a 
hardship  to  the  patient.  Excellent  extra-oral  radio- 
grams of  this  area  may  be  obtained,  providing  the  opera- 
tor has  the  ability  and  constancy  to  master  the  neces- 
sary technic. 

Root  Resection 

Where  root  resection  is  contemplated,  the  intelligent 
dentist  should  first  obtain  accurate  radiograms  of  the 


A. 


B. 


Fig.  82. — A,  upper  central  incisor  before  resection;  B,  radiogram  made  immedi- 
ately following  resection;  C,  radiogram  made  after  several  months,  showing  regen- 
eration  of  osseous  tissue. 

roots  under  consideration.  These  aid  him  greatlj^,  pri- 
marily in  determining  whether  or  not  a  resection  is  in- 
dicated, and  if  it  is,  it  will  give  him  a  fairly  concrete  idea 
of  the  field  of  operation  as  well  as  the  extent  of  the  root 
to  be  resected;  secondarily,  in  determining  whether  or 


INDICATIONS   FOR   X-RAY   IN   DENTISTRY 


163 


not  the  root  canal  lias  been  siifificiently  well  filled  so  that 
the  filling  extends  past  the  point  where  resection  is  to 
take  place. 

Following  root  resection,  a  radiogram  should  be  made 
as  a  matter  of  record  and  be  used  for  purposes  of  com- 
parison as  the  process  of  healing  progresses.  Subse- 
quently, additional  radiograms  should  be  made  every 
three  months  to  determine  whether  or  not  the  process 
of  bone-regeneration  is  progressing  in  a  satisfactory 
manner.    (See  Figs.  81,  82  and  83.) 


A.  B. 

Fig.  83. — A,  an  upper  central  root  before  resection;   B,  the  same  root  six  weeks  after 
resection,    showing   partial    regeneration. 

Radiographic  Requirements. — Intra-oral  radiograms 
should  be  used  exclusively.  In  fact,  the  necessity  for 
anything  else  could  hardly  arise,  as  root  resection  is 
usually  confined  to  the  anterior  teeth. 

For  Purposes  of  Examination  and  Diagnosis  in 
Pyorrhea  Alveolaris  and  Allied  Diseases 

A  radiographic  examination  of  the  teeth  and  their  in- 
vesting structures  is  of  great  advantage  in  diagnosis  and 
treatment.  In  the  first  place,  accurately  made  radio- 
grams will  often  show  the  extent  to  which  the  destruc- 
tive process  has  progressed,  especially  if  areas  of  ab- 


164 


DENTAL   AND   ORAL   RADIOGRAPHY 


sorption  and  ** pockets"  exist  upon  the  mesial  or  distal 
aspects  of  teeth.  Even  where  such  areas  are  visible 
to  the  eye,  the  radiogram  serves  an  important  function 
in  acquainting  the  patient  with  the  true  state  of  affairs, 
thereby  securing  the  patient's  cooperation  in  the  treat- 
ment.    (See  Fig.  84.) 

When  the  destructive  process  is  shoMm  to  be  exten- 
sive about  certain  teeth,  the  operator  can  more  safely 


Fig.    84. — A    well-clevtloped    case    of   pyorrhea  alvcolaris   involving   the    molars   and    in- 
cisors.     (After  Arthur  H.   Merritt.) 

judge  whether  or  not  the  treatment  of  such  teeth  should 
be  attempted  or  whether  they  should  be  extracted. 

Where  suppuration  is  occurring  at  the  gingival  margin, 
the  radiogram  is  often  indispensable  in  helping  to  deter- 
mine (by  showing  the  contents  of  the  root  canals) 
whether  the  adjacent  teeth  are  vital,  and  if  nonvital 
whether  or  not  the  suppuration  is  due  to  a  chronic  alveo- 
lar abscess. 


INDICATIONS    FOR   X-RAY    IN    DENTISTRY  165 

In  cases  of  gingival  irritation  about  crowned  teeth  or 
teeth  carrying  large  fillings  or  inlays,  a  radiogram  will 
reveal  jagged  or  overhanging  edges,  the  removal  of  which 
is  so  essential  if  the  tissues  are  to  be  restored  to  health. 

Finally,  the  radiogram  or  a  series  of  radiograms  will 
be  of  value  after  active  treatment  has  been  completed, 
to  determine  whether  or  not  the  destructive  process  has 
been  successfully  checked. 

Radiographic  Requirements. — Intra-oral  radiograms 
will  suffice  for  such  cases,  as  pockets  seldom  extend  be- 
low the  apical  area  of  the  roots.  Such  radiograms  should 
be  made  in  series,  so  that  no  area  about  the  teeth  is  left 
unsurveyed. 

In  Crown  and  Bridgework 

Where  teeth  are  to  be  crowned  individually,  or  as 
bridge  abutments,  the  radiogram  will  give  valuable  in- 
formation, not  only  as  to  the  length  and  shape  of  the 
roots,  and  the  condition  of  the  investing  structures,  but 
also  as  to  that  of  the  periapical  tissues.  Where  the  neces- 
sity for  the  devitalization  of  such  teeth  occurs,  the  op- 
erator can  also  judge  by  the  shape  and  condition  of  the 
roots  whether  or  not  the  prognosis  for  successful  root 
treatment  and  filling  is  favorable. 

Where  ''posts"  are  to  be  placed  in  the  roots,  their 
extent  and  direction  can  be  noted,  and  where  the  ana- 
tomic peculiarities  of  such  roots  make  them  liable  to 
perforation,  precautions  for  avoiding  such  calamities 
may  be  taken. 

AVhere  spaces  are  to  be  bridged,  and  the  exact  status 
of  the  area  which  is  to  lie  beneath  the  bridge  is  not 
known,  a  radiogram  should  be  made  to  be  sure  that  un- 
erupted  teeth  or  root  fragments  are  not  present.  (See 
Figs.  85,  86,  and  87.) 

Radiographic  Requirements. — Intra-oral  radiograms 
are  indicated  for  this  character  of  work. 


166 


DENTAL  AND   ORAL   RADIOGRAPHY 


Reflexes  of  Obscure  Origin 

Where  painful  reflexes  occur  about  the  face  or  head, 
and  a  clinical  examination  does  not  immediately  deter- 
mine their  possible  origin,  a  radiographic  examination 
of  the  teeth  and  their  adjacent  structures  is  indicated. 
Where  such  reflexes  are  the  result  of  unerupted,  im- 
pacted, or  anomalous  teeth,  the  presence  of  any  of  these 


Fig.  85. 


Fig.  86. 


Fig.  85. — An  unerupted  cuspid  tooth  making  an  attempt  to  erupt  under  a  bridge. 
The  patient  was  twenty-eight  years  of  age. 

Fig.  86. — Radiogram  made  to  be  sure  no  root  fragments  were  present  in  the  tis- 
sues  under   the   bridge. 


Fig.   87. — Inflammatory  process  under  a  small  bridge.     An   extensive  pocket  is   shown 
upon  the  mesial  aspect  of  the  root  of  the  bridge  abutment. 

is  quickly  demonstrated.  Likewise,  if  the  reflexes  are 
caused  by  an  alveolar  abscess,  its  presence  can  be 
thereby  determined. 

Where  pulp  stones  are  producing  the  trouble,  they  can 
often  be  detected,  if  intense  care  is  exercised  in  making 
the  radiograms.  If  these  reflexes  are  the  result  of  ''hid- 
den caries,"  the  radiogram  will  frequently  suggest  the 


i 


INDICATIONS   FOR   X-RAY    IN   DENTISTRY  167 

presence  of  such  a  condition,  providing  the  cavities  occur 
upon  the  mesio-or  disto-approximal  surfaces  of  the  teeth, 
and  are  sufficiently  extensive  so  that  the  density  of  the 
tooth  structure  in  the  region  of  the  cavity  is  decreased, 
or  the  contour  of  the  tooth  is  altered. 

Radiographic  Requirements. — Approximately  the 
same  plan  of  examination  should  be  used  as  where  a 
general  radiographic  examination  of  the  mouth  is  made ; 
viz.,  extra-oral  radiograms  of  each  side  with  intra-oral 
radiograms  of  the  anterior  teeth.  These  can  be  further 
augmented  with  confirmatory  intra-oral  radiograms,  if 
necessary.     (See  Figs.  72  and  73.) 

In  Oral  Surgery 

Perhaps  the  most  frequent  indication  for  the  use  of 
the  x-ray  in  oral  surgery  occurs  in  cases  in  which  the 
extraction  of  certain  teeth  is  necessary.  For  instance, 
if  one  or  more  third  molars  are  to  be  removed,  a  radio- 
gram of  these  teeth  and  their  surrounding  structures 
will  acquaint  the  operator  with  any  abnormalities  of  po- 
sition or  formation,  and  will  make  it  possible  to  proceed 
with  the  operation  without  unknown  handicaps. 

Following  the  removal  of  teeth,  a  radiogram  of  the 
field  of  operation  is  often  of  value  as  a  matter  of  record, 
to  make  sure  that  no  root  fragments  or  bone  fragments 
are  left  remaining. 

"Where  necrotic  areas  are  to  be  curetted,  a  radiogram 
not  only  aids  greatly  in  confirming  the  diagnosis,  but 
gives  the  operator  a  more  comprehensive  idea  of  the 
extent  to  which  the  curettement  must  be  carried  out.  As 
a  postoperative  precaution,  the  radiogram  is  also  fre- 
quently of  value,  especially  where  the  process  of  healing 
does  not  progress  in  a  manner  satisfactory  to  the  pa- 
tient or  operator.    Such  postoperative  radiograms  are 


168 


DENTAL   AND   ORAL   RADIOGRAPHY 


Fig.   88-^. 


Fig.  88-B. 
Fig.  88-^.  and  B. — F)xtra-oral  radiograms  of  ini])acted  and  unerupted  tiiird  molars. 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY 


169 


particularly  advantageous  where  patients  move  from  one 
locality  to  another,  and,  therefore,  must  change  surgeons. 

In  handling  fractures  of  the  mandible,  the  x-ray  is 
seldom  necessary  for  purposes  of  diagnosis,  but  it  can 
often  be  used  to  advantage,  and  in  some  instances,  is  quite 
indispensable.  As  a  postoperative  precaution  it  should 
be  used  so  that  no  doubt  may  arise  as  to  the  proper 
placement  of  the  fractured  parts. 

Where  fractures  of  the  maxilla  occur,  a  radiogram  may 
be  of  value  as  a  means  of  confirming  the  clinical  diag- 
nosis. 

Where  cysts  or  tumors  are  suspected,  the  radiogram 
will  confirm  the  clinical  findings,  and  comprehensively 


Vig. 


?. — -Intra-oral    radiograms    of    impacted    lower    third    molars.       Such    radiograms 
are  not  as  satisfactory  as  those  made  by  the  method  shown  in   Fig.  95. 


outline  the  field  of  operation.  Following  operations  for 
the  relief  of  those  conditions,  radiograms  should  be  made 
at  frequent  intervals  to  determine  whether  or  not  the 
process  of  healing  is  progressing  satisfactorily. 

In  gunshot  wounds  about  the  face  or  mouth,  properly 
made  radiograms  will  localize  the  bullets  or  shot,  and 
thereby  aid  in  their  removal,  as  well  as  in  determining 
the  extent  of  injury  to  the  osseous  structures. 

Where  drills,  hypodermic  needles  or  other  instruments 
are  broken  off  and  left  remaining  in  the  tissues,  they  may 
be  easily  located  by  correctly  made  radiograms,  and  their 
removal  rendered  more  certain. 


170 


DENTAL   AND   ORAL   RADIOGRAPHY 


Fig.   90-A. — Il,arge  cyst   in  the  mandible  lying  below  a  molar  tooth. 


Fig.    90-B. — Same    case    six    months    after    curettemer.t,    showing    partial    regeneration 
of  the  osseous  structure. 


I 


INDICATIONS    FOR   X-RAY    IN   DENTISTRY 


171 


Radiographic  Requirements. — Both  the  extra-oral  and 
intra-oral  radiograms  are  indicated  in  this  field.  For 
impacted  third  molars,  the  extra-oral  method  is  best,  as 
it  will  clearly  show  not  only  the  third  molar,  but  its  re- 
lationship to  all  other  adjacent  structures.  In  the  case 
of  single-rooted  teeth,  such  as  incisors,  cuspids,  etc., 
where  hypercementosis  is  suspected,  the  intra-oral 
method  will  prove  adequate.     (See  Figs.  88,  89  and  90.) 

Where  a  curettement  is  to  be  carried  out,  intra-oral 
radiograms  will  prove  sufficient,  provided  the  field  is  not 
large.     (Fig.  91.) 


Fig.    91. — L,arge   abscess   v/ith   cyst   formation   involving  the   upper   central,    lateral   and 

cuspid   roots. 

In  fractures  of  the  mandible,  the  extra-oral  method 
should  always  be  used,  so  that  the  entire  field  in  the  re- 
gion of  the  fracture  can  be  visualized. 

For  fractures  of  the  maxilla,  intra-oral  radiograms 
will  usually  suffice. 


In  the  Practice  of  Orthodontia 

The  necessity  for  using  the  x-ray  in  orthodontic  prac- 
tice varies  with  different  patients,  but,  generally  speak- 
ing, may  be  summarized  under  ten  different  headings  as 
follows : 

1.  As  a  means  of  determining  the  presence  or  ah- 


172 


DENTAL   AND   ORAL   RADIOGRAPHY 


Fig.    92. — This   ratliograni   reveals   the   fact   that   there   is   a   congenital   absence   of   per 
manent    molars    on    the    left    side. 


Fig.   93. — This   radiogram    reveals   the   fact   that   all   but    one   of  the   permanent    molars 
are  congenitally  absent  on   the  right  side. 


INDICATIONS    FOR   X-RAY    IN    DENTISTRY  173 

se7ice  of  unerupted  permanent  teeth  before  treatment  is 
undertaken. 

The  majority  of  patients  requiring  orthodontic  treat- 
ment usually  have  a  mixed  dentition ;  viz.,  the  deciduous 
molars  and  cuspids  are  usually  present.  It  is  essential, 
therefore,  to  determine  whether  or  not  these  deciduous 
teeth  have  their  permanent  successors.  If  the  upper  and 
lower  incisors  have  erupted,  information  concerning  the 
other  permanent  teeth  is  easily  obtained  by  making  a 
radiogram  of  each  side  by  the  extra-oral  method.  Such 
radiograms  are  shown  in  Figs.  92  and  93. 

Such  radiograms  give  the  operator  a  very  adequate 
survey  of  these  unerupted  teeth,  and  leave  no  doubt  as  to 
their  presence  or  absence. 

2.  As  a  means  of  determining  the  approximate  size 
of  unerupted  teeth,  for  ivhich  space  must  he  made  in  the 
arches. 

Where  the  deciduous  molars  or  cuspids  have  been  shed 
prematurely,  with  the  usual  resultant  loss  of  space  in  the 
arch,  the  radiogram  can  be  made  to  show  quite  accurately 
the  amount  of  space  which  it  will  be  necessary  to  pre- 
pare for  the  unerupted  teeth.  (See  Figs.  94,  95  and 
96.) 

3.  To  determine  the  state  of  development  of  unerupted 
teeth  ivhich  are  tardy  in  their  eruption. 

Not  infrequently  permanent  teeth  fail  to  erupt  when 
expected.  By  utilizing  the  radiogram,  their  state  of  de- 
velopment is  easily  determined,  and  often  the  cause  for 
their  noneruption  is  determined.  Steps  can  then  be  taken 
to  open  up  spaces  and  to  hold  them  until  such  a  time  as 
the  teeth  involved  progress  in  their  development  to  the 
point  of  eruption.  (See  Fig.  97.) 

4.  To  determine  the  approximate  direction  in  ivhich 
teeth  are  erupting  and  the  relationship  which  they  will 
hear  to  the  line  of  occlusion  when  erupted. 


174 


DENTAL   AND   ORAL   RADIOGRAPHY 


Fig.   94. — Unerupted   lower  second  bicuspid   for   which   sjiace   must   be   made   to   permit 

its   eruption. 


pp 

w    ^ 

^^^^^^^^^^^^^-^ 

\U*^  _ 

^H 

fl 

B 

j    %. ^^H 

Fig.    95. — Unerupted   cuspid    for   which    space    must   be    made    if   it    is    to    ertipt   in    its 

normal  position. 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY  175 


Fig.    96. — Unerupted    lower    lateral    incisor    for    which    space    must    be    made. 


Fig.   97. — Unerupted   lower  second  molar  prevented   from  erupting  through  impaction 
against  the  lower  first  molar. 


176 


DENTAL    AND    ORAL   RADIOGRAPHY 


Where  the  deciduous  teeth  have  been  retained  in  the 
mouth  longer  than  the  normal  time  and  where  the  roots 
of  these  teeth  have  not  been  entirely  absorbed,  the  erupt- 
ing permanent  teeth  will  sometimes  be  deflected  from 
their  normal  course.  It  is  an  advantage  to  know  the  di- 
rection in  which  they  are  deflected,  so  that  if  retaining 
appliances  are  to  be  placed,  they  may  be  arranged  in 


l'"ig.   98. — Unenipted  upper  bicuspid  teeth  which  are  being  deflected  to  the  lingual. 


A.  \  B. 

Fig.    99. — Unerupted    bicuspid    teeth    which   are    rotated    and    erupting    to    the    lingual. 


such  a  way  and  in  such  a  relationship  to  the  erupting 
teeth  that  they  will  not  interfere  with  them.  In  fact, 
it  is  sometimes  possible  to  construct  the  retainer  in  such 
a  way  that  the  tooth  which  is  deflected  from  its  course 
may  be  guided  towards  its  normal  position  or  moved 
there  before  the  inclined  planes  of  the  opposing  teeth  be- 
come a  factor  in  establishing  it  entirely  out  of  its  normal 
position.     (See  Figs.  98  and  99.) 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY 


177 


Fig.  100. — A,  unerupted  cuspid;  B,  same  tooth  after  the  removal  of  the  lateral 
incisor  and  the  deciduous  cuspid  showing  the  attachment  for  moving  the  unerupted 
tooth;   C,  cuspid  tooth  moved   down   to   the  point  of  eruption. 


A. 


B. 


Fig.    101. — A,    two    supernumerary    incisors    are    present  with    the    normal    central 

lying  above  them;   B,  the  same  case  after  the  extraction  of  the  supernumerary   teeth. 

An   attachment    has    been    made    to    the    central    preparatory  to    moving    it   down    into 
place.      The   patient   was    fourteen   years   of   age. 


178  DENTAL   AND   ORAL   RADIOGRAPHY 

5.  As  a  guide  where  it  is  necessary  to  make  attach- 
ments to  unerupted  teeth,  to  aid  in  their  eruption. 

While  it  is  not  often  necessary  to  secure  attachments 
to  teeth  lying  beneath  the  gingival  tissues,  the  occasion 
for  this  sometimes  arises,  as  shown  in  Figs.  100  and  101. 
In  such  cases,  radiograms  should  be  made  as  a  guide  in 
securing  the  attachment.  After  the  attachment  is  se- 
cured, others  should  be  made  to  determine  the  direction 
in  which  force  should  be  applied  to  accomplish  the  desired 
tooth  movement. 

6.  To  determine  the  most  opportune  time  for  the  ex- 
traction of  the  deciduous  teeth. 

Where  the  deciduous  tooth  persists  in  the  mouth,  and 
shows  no  sign  of  being  shed,  it  is  an  advantage  to  deter- 
mine the  extent  of  absorption  of  the  roots,  as  well  as  the 
development  of  its  successor,  so  that  if  extraction  is  re- 
sorted to,  it  can  be  done  with  the  knowledge  that  the  de- 
veloping tooth  will  not  be  disturbed  or  injured,  and  that 
the  successor  has  reached  a  degree  of  development  which 
will  insure  its  eruption  within  a  reasonable  time.  (See 
Figs.  102  and  103.) 

7.  To  observe  the  movement  of  the  roots  of  teeth  and 
their  relationship  to  other  roots  and  structures. 

In  the  bodily  movement  of  teeth,  and  particularly  of 
the  incisors,  it  is  important  in  young  subjects  that  these 
roots  do  not  encroach  upon  each  other  or  upon  other 
teeth;  for  instance,  an  unerupted  cuspid.  It  is  there- 
fore, advisable,  where  any  doubt  exists,  to  determine  the 
exact  status  of  this  relationship.     (See  Fig.  104,  A,  B,  C.) 

8.  To  determine  the  relationship  of  developing  third 
molars  to  certain  recurrent  malocclusions,  and  also  as  a 
precaution  so  that  steps  may  he  taken  to  prevent  these 
teeth  from  becoming  a  cause  of  malocclusion  during  their 
eruption. 

The  pressure  exerted  by  developing  lower  third  molars 


INDICATIOiSrS    FOR    X-RAY    IN"    DENTISTRY 


179 


Fig.    102. — An    unerupted    lower    second    bicuspid    in    a    patient    twelve    years    old. 


Fig.    103. — Unerupted    upper   and    lower   bicuspids    in   a   patient   eleven    years   of   age. 


180 


DENTAL  AND   ORAL   RADIOGRAPHY 


is  often  sufficiently  great  to  cause  a  crowding  of  the  lower 
incisors  and  cuspids.  (See  Figs.  105  and  106.)  This 
can  be  true,  even  though  malocclusion  has  not  existed 
in  this  region  previous  to  the  development  of  the  third 
molars.  By  making  radiograms  from  time  to  time  of 
patients  at  the  age  of  the  eruption  of  these  teeth,  the 
status  of  the  developing  teeth  can  be  determined  and  the 


Fig.    104. — Unerupted    cuspid    teeth    whose    relationship    to    the    roots    of    the    incisois 
must  be  taken  into  consideration  during  tooth   movement. 

necessary  precautions  taken  to  prevent  the  crowding  of 
the  incisors  and  cuspids. 

9.  To  observe  nonvital  teeth  prior  to  tooth  movement, 
to  determine  their  fitness  for  movement  or  anchorage, 
and  their  state  of  health  during  the  process  of  ortho- 
dontic treatment. 


INDICATIONS   POR   X-RAY   IN   DENTISTRY 


181 


Fig.    105. — An   unerupted    lower    third    molar   which   is   crowding   the   incisors. 


Fig.  106. — An  erupting  lower  third  molar  which  has  been  responsible  for  the  crowding 
of  the   lower   incisors  and   cuspids. 


182  DENTAL   AND   ORAL   RADIOGRAPHY 

Where  it  is  necessary  to  either  move  nonvital  teeth,  or 
utilize  them  as  anchorage,  it  is  essential  to  the  patient's 
welfare  and  comfort  to  know  that  snch  teeth  and  their 
investing  tissues  are  in  a  healthy  condition.  By  determin- 
ing this  prior  to  instituting  orthodontic  treatment,  much 
trouble,  both  to  the  patient  and  operator,  can  often  be 
avoided.     (See  Fig.  107.) 

10.  In  cases  tvhere  anomalous  teeth  are  present,  to  dif- 
ferentiate hetiveen  anomalous  and  normal  teeth. 

In  a  majority  of  instances,  this  can  be  done  without  the 
aid  of  the  radiogram,  unless  the  teeth  in  question  have 
failed  to  erupt.  Under  such  conditions,  by  utilizing  ac- 
curacy in  the  technic  of  making  the  radiograms,  little  dif- 
ficulty is  encountered  in  determining  the  difference  be- 
tween normal  and  anomalous  teeth.  Examples  are  shown 
in  Figs.  108,  109  and  110. 

Radiographic  Requirements. — Owing  to  the  fact  that 
patients  undergoing  orthodontic  treatment  are  usually 
children  whose  ages  necessitate  their  being  handled  with 
tact  and  gentleness,  if  confidence  is  to  be  maintained, 
precaution  should  be  taken  to  rid  every  operation  of 
fear  or  discomfort.  Especially  is  this  essential  in  mak- 
ing radiograms,  for  any  considerable  degree  of  move- 
ment on  the  part  of  a  patient  will  either  curtail  the  value 
of  the  finished  radiogram,  or  render  it  useless. 

In  selecting  a  method  of  procedure  for  making  radio- 
grams of  children,  the  child's  comfort  must  be  taken 
into  consideration,  and  with  this  idea  in  mind,  the 
author  has  found  it  an  advantage  to  use  the  extra-oral 
method  quite  universally.  In  fact,  he  has  used  it  in 
nearly  all  cases  except  where  the  region  embracing  the 
upper  anterior  teeth  is  under  scrutiny.  The  wisdom  of 
this  course  will  be  apparent  to  anyone  who  has  experi- 
enced the  discomfort  of  having  intra-oral  films  placed 
lingually  to  the  lower  teeth,  where  the  tissues  are  very 


INDICATIONS   FOR   X-RAY   IN   DENTISTRY 


183 


Fig.    107. — A,   nonvital   tooth   being  used  as  an   anchor  tooth;   B,   nonvital   tooth   which 
was  not  considered  safe  for  anchorage. 


Fig.    108. 


Fig.    109. 


Fig.  108. — Supernumerary  upper  second  bicuspid.  Upon  the  extraction  of  the 
supernumerary,   the   normal    tooth  erupted. 

Fig.  109. — Lower  deciduous  central  incisors  having  the  appearance  of  supernu- 
merary teeth.  The  radiogram  leaves  no  doubt  as  to  their  identity,  and  also  shows 
that  these  teeth  have  no   permanent   successors. 


Fig.    110. 

Fig.  110. — Radiogram  showing  either  an  anomalous  central  incisor  or  a  central 
incisor  lying  in  a  horizontal  position  to  the  other  teeth.  The  patient  was  sixteen 
years  of  age. 


184 


DENTAL   AND   ORAL   RADIOGRAPHY 


Fig.   111. — The  patient   is  seated   and  the  apparatus  arranged   to  mai<e   a   radiogram 
of   the  left  side.     Fig.   99  shows  the  extent  of  radiograms   made   by  using  this  technic. 


Fig.   112. — The  patient  is  seated  and  the  apparatus  is  arranged  to  make  a  radiogram 
of  the  right  side.     Fig.   100  shows  the  extent  of  radiograms  made  by  using  this  technic. 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY  185 

sensitive,  or  has  had  them  placed  posteriorly  in  the 
molar  region,  against  the  palate,  where  they  so  fre- 
quently induce  gagging.  These  unpleasant  features  are 
all  eliminated  by  using  the  extra-oral  method,  and  good 
radiograms  of  the  structures  can  be  secured  on  the 
larger  plates.  (See  Figs.  Ill  and  112.)  This  statement 
should  not  be  construed  as  a  protest  against  the  use  of 
intra-oral  films  in  dental  radiography,  for  it  is  very 
often  necessary  to  use  such  films  with  adult  patients 
where  a  high  degree  of  detail  is  essential,  in  determin- 
ing the  condition  about  nonvital  teeth,  root  canal  fillings, 
etc.  In  orthodontic  practice,  however,  where  we  are 
dealing  with  young  subjects  entirely,  a  sufficient  degree 
of  detail  can  be  obtained  in  the  majority  of  instances  to 
satisfy  the  needs  of  the  operator,  by  using  the  extra-oral 
method. 


CHAPTER  XII 

DANGERS   OF   THE  X-RAY  AND   METHODS   OF 
PROTECTION 

Almost  invariably  when  any  phase  of  x-ray  work  is 
discussed,  some  one  raises  the  query  as  to  the  dangers 
connected  with  it  and  the  injuries  resulting  from  its  use. 
In  fact,  the  impression  is  still  quite  broadcast  among  the 
laity,  and  to  a  degree  among  the  profession,  that  the 
x-ray  is  a  dangerous  agent  and  as  such  should  only  be 
employed  in  cases  of  dire  emergency. 

This  impression,  erroneous  as  we  know  it  to  be  for 
the  most  part,  gained  credence  as  a  result  of  the  first 
few  years'  use  of  the  x-ray,  during  which  period  its 
dangers  were  not  suspected  nor  the  laws  governing  its 
use  well  understood.  During  this  period  a  sufficient 
number  of  patients  and  operators  were  injured  so  that, 
notwithstanding  the  fact  that  with  our  present  knowl- 
edge of  the  subject  and  with  the  marked  improvement 
in  x-ray  apparatus  these  accidents  are  no  longer  neces- 
sary, the  early  impression  still  prevails  to  a  certain 
extent. 

In  order  that  we  may  not  underestimate  the  dangers 
of  this  valuable  agent  and  consider  lightly  our  responsi- 
bility in  using  it,  we  will  now  consider  the  character  of 
injuries  possible  through  its  misuse. 

We  should  bear  in  mind  the  fact  that  the  x-ray  in 
medicine  serves  a  double  purpose.  It  is  used  as  a  diag- 
nostic agent;  that  is,  in  making  radiograms  and  fluoro- 
scopic examinations,  and  as  a  therapeutic  agent.  In  the 
latter  capacity  patients  are  subjected  to  repeated  ex- 
posures, the  length  of  which  are  very  far  in  excess  of 

186 


X-RAY   DANGERS METHODS    OF    PROTECTION  187 

that  required  in  making  radiograms.  In  fact  the  length 
of  exposure  in  one  average  x-ray  therapy  treatment  will 
more  than  out-total  the  necessary  exposures  to  radio- 
graph a  half  dozen  patients  for  diagnostic  purposes. 
Therefore,  the  responsibility  of  the  x-ray  therapist,  and 
the  danger  connected  with  his  work  are  far  in  excess  of 
the  man  who  limits  his  activities  with  x-ray  to  radiog- 
raphy alone. 

Of  the  various  ill  effects  attributed  to  the  x-ray,  the 
so-called  "x-ray  burn"  or  dermatitis  is  the  most  com- 
mon. This  injury  occurs  in  various  degrees  of  severity, 
depending  upon  the  amount  of  overexposure  to  which 
the  one  afflicted  has  been  subjected,  and  is  designated  as 
"acute"  and  "chronic." 

Acute  X-ray  Dermatitis 

Acute  x-ray  dermatitis  in  its  simplest  form  manifests 
itself  in  somewhat  the  same  way  as  ordinary  sunburn. 
There  is  a  slight  pinkish  erythema,  dry  in  character, 
accompanied  oftentimes  by  the  sensation  of  tingling  or 
burning.  If  x-ray  exposures  are  continued,  this  condi- 
tion is  augmented  by  the  appearance  of  vesicles  and  the 
affected  surface  becomes  moist  or  "weeping,"  and  the 
patient  has  similar  sensations  as  those  produced  by  any 
blistering  burn.  If  exposures  to  the  ray  be  discontinued 
at  this  stage,  the  affected  area  will  slowly  clear  up  with 
no  permanent  ill  effect  except  perhaps  a  slight  pig- 
mentation. 

If  the  exposures  be  continued,  the  next  degree  of  der- 
matitis will  ensue.  The  affected  area  becomes  an  angry 
red  in  appearance,  congestion  is  intense,  and  the  surface 
is  covered  with  a  yellowish  white  necrotic  membrane, 
which  is  epithelial  in  character.  In  fact,  up  to  this  point 
the  connective  tissue  is  not  affected  except  for  more  or 
less  swelling.    This  degree  of  dermatitis  is  exceedingly 


188  DENTAL   AND   ORAL   RADIOGRAPHY 

slow  in  healing,  months  being  required  for  the  necrotic 
membrane  to  disappear,  and  when  this  has  occurred  it  is 
followed  by  a  horny  epidermis  which  appears  in  spots 
over  the  area  affected,  eventually  covering  it.  This  new 
skin  while  smooth  and  natural  looking  is  usually  char- 
acterized by  the  absence  of  all  hairs  and  follicles. 

The  most  severe  form  of  acute  x-ray  dermatitis  is  char- 
acterized by  somewhat  the  same  symptoms  as  those  just 
described,  except  that  they  are  greatly  exaggerated. 
The  degree  of  congestion  is  very  great,  the  necrotic 
membrane  extends  deeper  into  the  tissue,  necessitating 
the  surgical  removal  of  masses  of  dead  tissue  to  prevent 
gangrene.  This  sloughing  or  necrotic  area  shows  a 
strong  tendency  to  spread  and  according  to  some 
authors,  is  apt  to  become  malignant.  With  such  a  der- 
matitis patients  often  suffer  very  intense  pain.  Inju- 
ries of  this  degree  of  intensity  are  exceedingly  slow  in 
healing,  a  number  of  years  sometimes  being  necessary 
for  the  process  of  reconstruction.  Even  after  it  occurs, 
the  skin  is  not  natural  in  appearance,  but  hard  and 
horny  and  covered  in  places  with  scar  tissue. 

Chronic  X-ray  Dermatitis 

After  a  person  has  been  exposed  to  the  x-ray  a  great 
many  times  covering  a  period  of  perhaps  months  or 
years,  and  has  had  one  or  more  "burns"  which  were 
not  allowed  to  heal  before  new  effects  were  added  by 
additional  exposures,  the  dermatitis  which  results  be- 
comes "chronic."  This  chronic  x-ray  dermatitis  is  con- 
fined almost  entirely  to  x-ray  operators  and  others  con- 
stantly associated  with  the  x-ray.  The  hands  because  of 
their  exposed  position  are  most  often  the  seat  of  this 
affection.  The  skin  becomes  thin  and  atrophic  with  red 
patches  of  a  vascular  nature,  and  there  is  usually  an 
entire  absence  of  all  follicles  and  hair.  Codman  describes 


X-RAY   DANGERS METHODS    OF    PROTECTION  189 

this  condition  as  follows:  "In  the  less  pronounced 
forms  the  skin  appears  chapped  and  roughened,  and  the 
normal  markings  are  destroyed ;  at  the  knuckles  the  folds 
of  skin  are  swollen  and  stiff,  while  between  there  is  a 
peculiar  dotting  resembling  small  capillary  hemorrhages. 
The  nutrition  of  the  nails  is  affected  so  that  the  longi- 
tudinal striations  become  marked  and  the  substance  be- 
comes brittle.  If  the  process  is  more  severe,  there  is  a 
formation  of  blebs,  exfoliation  of  epidermis,  and  loss  of 
nails.  In  the  w^orst  form  the  skin  is  entirely  destroyed 
in  places,  the  nails  do  not  reappear  and  the  tendons 
and  joints  are  damaged." 

Another  author  states  that  "while  the  condition  in 
chronic  forms  of  x-ray  irritation  is  as  a  whole  atrophic, 
there  is  usually  a  peculiar  tendency  to  hyperkeratosis, 
which  shows  itself  in  increased  horniness  of  the  epi- 
dermis about  the  knuckles  and  in  the  formation  of  kera- 
totic  patches.  In  some  cases  this  is  very  marked,  so  that 
the  affected  parts,  usually  the  backs  of  the  hands,  have 
scattered  over  them  many  keratoses  with  or  without  in- 
flamed bases.  The  appearance  is  very  similar  to  that 
seen  in  senile  keratosis  where  the  patches  are  inflamed 
and  have  a  tendency  to  epitheliomatous  degeneration. 
The  development  of  epitheliomas  in  these  patches  of  x- 
ray  keratosis  has  within  the  last  few  years  been  well 
established."  Carcinoma  may  also  have  its  origin  from 
the  same  source,  in  fact  many  x-ray  operators  who  have 
failed  to  take  the  proper  precautions  have  been  subject 
to  this  dreaded  malady,  the  hands  being  the  parts  most 
often  affected. 

Other  111  Effects 

In  addition  to  the  before  described  injuries,  there  are 
still  other  ill  effects  attributed  to  the  x-ray,  such  as  loss 
of  hair,  sterility,  and  certain  systemic  effects.    The  loss 


190  DENTAL   AND   ORAL   RADIOGRAPHY 

of  hair  due  to  x-ray  exposure  is  not  to  be  regarded  seri- 
ously, unless  it  is  associated  with  a  dermatitis  of  suffi- 
cient severity  to  destroy  the  hair  follicles,  for  unless  this 
complication  is  present,  the  hair  comes  back  within  five 
or  six  weeks. 

The  x-ray  has  a  deleterious  effect  upon  developing  em- 
bryonic cells  and  can  therefore  be  the  cause  of  sterility 
in  the  male  by  destroying  the  spermatozoa,  and  in  the 
female  by  the  destruction  of  the  primordial  ovules.  This 
condition  is  brought  about  by  continued  exposures,  and 
x-ray  operators  are  the  ones  usually  affected.  It  is  not 
accompanied  by  impotence,  is  temporary  in  duration, 
and  can  be  avoided  entirely  by  adopting  protective 
measures. 

Regarding  the  so-called  injurious  systemic  effects  pro- 
duced by  the  x-ray,  too  little  evidence  of  a  convincing 
character  has  yet  been  presented  to  really  fasten  the 
blame  upon  the  x-ray  for  conditions  other  than  those 
before  enumerated.  Therefore,  until  its  guilt  is  scien- 
tifically substantiated,  we  must  not  indict  it  for  condi- 
tions which  may  be  but  coincident  with  its  use. 

Methods  of  Protection 

The  evil  effects  of  the  x-ray  can  be  entirely  avoided  by 
utilizing  the  protective  measures  afforded  in  modern  x- 
ray  apparatus.  Inasmuch  as  lead  is  impervious  to  the 
rays,  it  can  be  used  in  different  forms  and  in  various 
pieces  of  apparatus  in  such  a  way  as  to  control  or  con- 
fine the  rays  according  to  the  will  of  the  operator. 

Tube  Shield 

The  most  essential  piece  of  protective  apparatus  is 
the  tube  shield  (Fig.  113).  This  is  constructed  of  lead 
glass,  there  being  a  sufficient  amount  of  lead  salts  incor- 
porated in  the  glass  to  prevent  ordinary  rays  from  pass- 


X-RAY   DANGERS — METHODS   OF   PROTECTION 


191 


ing  through  it.  The  sides  extend  up  over  the  highest 
part  of  the  tube  and  the  opening  at  the  top  is  often  cov- 
ered with  a  rubber  cap,  in  which  lead  is  also  incorporated. 
At  the  bottom  directly  opposite  the  target  of  the  tube  an 
opening  of  the  proper  size  is  left  to  allow  the  desired 
rsijs  to  pass  out.  The  size  of  this  opening  may  be  con- 
trolled by  interchangeable  diaphragms  of  various  sizes, 
which  are  constructed  of  sheet  lead  about  one-sixteenth 
of  an  inch  in  thickness. 


Fig.    113. — An   x-ray   tube   inclosed   within   a  leaded   glass  tube   shield. 

This  apparatus  is  usually  augmented  by  a  compres- 
sion cylinder,  which  is  attached  to  the  base  of  the  tube 
shield,  against  or  in  contact  with  the  lead  diaphragm. 
Such  a  cylinder  is  usually  constructed  of  aluminum  with 
a  lead  lining,  is  made  in  various  lengths  and  diameters 
according  to  the  character  of  the  work  for  which  it  is  to 
be  used,  and  serves  the  purpose  of  confining  the  rays 
coming  through  the  diaphragm  from  the  target  of  the 
tube. 


192 


DENTAL   AND   ORAL   RADIOGRAPHY 


These  pieces  of  apparatus  are  usually  integral  parts 
of  the  modern  tube  stand,  sold  by  all  reliable  manufac- 
turers of  x-ray  apparatus.  It  should  be  apparent  to 
anyone  that  with  such  apparatus,  the  only  rays  which 
leave  the  area  of  the  tube  are  those  which  pass  through 


Fig.     114. — lyead-Iined    protection    screen. 


the  diaphragm  and  cylinder  and  are  used  upon  the  pa- 
tient.    In  radiographic  work  these  do  not  injure  the 
patient,  as  the  exposures  are  too  short  to  produce  ill 
effects,  even  if  numerous  exposures  are  necessary. 
On  the  other  hand  the  radiographer  who  fails  to  use 


X-RAY    DANGERS METHODS    OF    PROTECTION  193 

these  protective  measures,  or  Avho  carelessly  places  him- 
self in  the  direct  path  of  the  rays  will  in  time  through 
the  accumulative  effect  of  the  x-ray  be  very  apt  to  reap 
as  a  result  of  his  folly  some  of  the  dread  injuries  before 
described. 

Other  Means  of  Protection 

In  addition  to  the  protective  measures  thus  far  de- 
scribed, there  are  other  means  that  afford  additional  pro- 
tection, and  if  a  person  is  working  constantly  with  the 
x-ray  these  should  be  used.  Among  these  is  the  leaded 
screen  behind  which  the  operator  stands  during  the  time 
exposures  are  made  (Fig.  114).    Such  a  screen  is  usually 


^^ 


Fig.    115.-    r.tail-impregnaled   glove. 

placed  in  front  of  the  controlling  apparatus  and  has  a 
leaded  glass  window,  so  that  the  operator  can  watch  the 
patient  during  the  exposure.  Lead-impregnated  gloves 
(Fig.  115)  and  aprons  (Fig.  116)  are  also  used  by  some 
as  a  precaution,  but  such  extreme  measures  are  not  nec- 
essary for  the  dentist  doing  his  own  radiography. 

With  a  properly  constructed  leaded  glass  tube  shield, 
lead  diaphragm,  and  lead-lined  cylinder  the  operator  is 
safe,  provided  he  takes  the  precaution  of  avoiding  the 
direct  rays. 

We  all  realize  that  many  very  useful  agents  in  medi- 
cine and  surgery  are  dangerous  when  used  carelessly, 
indiscriminately,  or  may  we  say  ignorantly.    The  old  say- 


194  DENTAL   AND   ORAL  RADIOGRAPHY 

ing  that  * '  fools  rush  in  where  angels  fear  to  tread, ' '  per- 
haps applies  with  greater  significance  in  many  branches 
of  medicine  than  we  would  care  to  admit.  But  the  fact 
that  through  the  misuse  of  dangerous  agents,  many- 
patients  have  met  death,  or  have  been  subjected  to  need- 
less suffering,  is  no  argument  against  their  use  when 


Fig.     116. — X-ray    protection    apron. 

placed  in  competent  hands.  In  such  hands  the  x-ray 
stands  today  as  one  of  the  greatest  adjuncts  to  the  mod 
ern  art  of  healing,  a  blessing  to  humanity,  even  if  in  its 
early  history  it  left  its  martyrs  here  and  there ;  its  bene- 
fits and  triumphs  far  out-balance  any  evils  connected  with 
its  use. 


INDEX 


Alternating  current,  32 

Alveolar  abscesses,  142,  143 

Ampere,  33 

Anode,  27 

Anomalous  teeth,  151,  182 

Arrangement  of  apparatus,   73,  90 

B 

Broken-oft  broaches,  153 

C 
Cathode,  27 
Cathode  rays,  28,  29 
Coil,  38,  39 

primary,  44,  45 

secondary,  44,  45 
Compression  cylinder,  72 
Compression  cylinder,  special,  85 
Compression  diaphragm,  72 
Coolidge  tube,  (38,  ll(j 
Crookes,  Sir  William,  27 
Crookes'  tubes,  28 
Crown  and  bridgework,  165 
Current  conditions  for  radiography, 

no 

Cysts  and  tumors,  143,  144 

D 

Dangers  of  the  x-ray,  186 
Darkroom,  75 
portable,  75 
Developer  for  plates  and  films,  129 
Development  of  plates  and  films,  127 
Drying  plates  and  films,  129 

E 

Electric  currents,  32 
alternating,  32 


Electric  currents — Cont  'd. 

amperage,  33 

direct,  32 

high  tension,  32 

voltage,  32 

wattage,  33 
Electrolytic  interrupter,  48 
Electromagnetic  induction,  40 
Electromagnets,  39 
Electromotive   force,   32 
Electrons,  23 
Extra-oral  radiograms,  93 

F. 

Faraday,  Michael,  26 

Filling    materials,     appearance    of, 

153 
Film  holders,  87 
Films,  x-ray,  125 

film  chest,  124 

preparation  for  exposuie,  123 
Fluorescence,  27 
Fractures,  151 


Geissler,  27 


G 


H 


Hertz,  Heinrich,  28 
High  frequency  coils,  52 

diagrams  of,  53 
Hittorf,  27 
Hydrogen  tube,  67 

I 

Illuminating  cabinets,  135 
Impacted  teeth,  168 
Induced  currents,  39,  40 
Induction  coils,  44 
diagram  of,  45,  49 


195 


196 


INDEX 


Induction  coils — Oont  M. 

essential  parts  of,  44 

illustrations  of,  50 
Interpretation  of  radiograms,  133 
Inter rupterless  transformer,  54 

illustrated,  55 
Interrupters,  47 

electrolytic,  47 

mechanical,  47 
Intraoral  radiograms,  81,  82 

L 
Lead  apron,  194 

Lead  compression  diaphragm,  72-191 
Lead  gloves,  193 
Lead  screen,  192 
Leaded  glass  tube  shield,  72,  191 
Lead-lined  compression  cylinder,   71 
Lines  of  force,  magnetic,  37 
Low  vacuum  tubes,  113 

M 

Magnet,  electro,  38 

poles  of,  36 
Magnetic  effect   of  electric  current, 

38 
Magnetic  field,  36 
Magnetic  force,  lines  of,  37 
Magnetic    induction,    37 
Magnetism,  35 
Milliamperemeter,  112 
Missing  teeth,  171 

N 
Nature  of  the  x-ray,  23,  31 
Necrosis,  148 

O 

Ohm,  defined,  33 
Ohm  's  law,  34 
Oral  examination,   154 
Oral  surgery,  167 
Orthodontia,  171 

radiographic  requirements  in,  182 


Pathoradiography,  21 
Penetration  of  x-rays,  113 


Pericemental  infection,  156 
Photograpiiic  darkroom,  75 
Plate  chest,  124 
Plates,  x-ray,  123 

care  of,  124 

development  of,   127 

drying,  128 

preparation  of,  124 
Portable  darkroom,  75 
Power  rating  of  coils,  51 
Primary  coil,  44 
Protection  from  x-rays,  190 
Pyorrhea  pockets,  151,  163 

B 

Radiogram,  21,  77 

examination  of,  138 

extra-oral,  93 

interpretation  of,   133 

intra-oral,  80,  81 

projier    tube    and    current    condi- 
tions for,  113,  114 

rules  for  making,  82 
Radiographic  examination,  complete, 

108 
Rectifier,  chemical,  51 
Rhumkorfi."  coil,  44 
Roentgen,  William  Conrad,  25 
Roentgenogram,  21 
Roentgenograph,  21 
Roentgenology,  21 
Root  canal  treatment,  158 
Root  resection,  162 
Rotary  converter,  54 

S 

Secondary  coil,  44 
Self-induction,  43 
Solenoid,  38 
Spark  gap,  51 


Technic  of  radiography,  77,  93,  110 
correct  and  incorrect,  diagram  of 

82 


INDEX 


]97 


Toriiiiiiology,  20 
Tesla  coils,  52 

Transformers,  iuterrupterless,  54 
Tube,  connection  to  x-ray  machine, 
63 

inverse  in,  116 

regulation  of,  114 
Tube  conditions  for  radiograms,  110 
Tube  shield,  72 
Tube  stand,  69 

with  platerest,  98 
Tubes,  low,  medium,  and  high,  11  J! 

U 

Unerupted  teeth,  173 

Unit  of  electromotive  force,  32 

current  strength,  33 

resistance,  33 

V 

Vacuum  of  tube,  how  to  determine, 
111 
relative    merits    of    low,    medium, 
and  high,  113 


Vacuum  tubes,  63,  110 
Volt,  32 
Voltage,  32 

W 
Watt,  33 
Wattage,  33 

X 

X-ray,  dangers  of,  1S6 
defined,  24 
dermatitis,   acute,   187 

chronic,  188 
discovery  of,  25 
effect    upon    photographic   plates, 

31 
machines,  44 
nature  of,  23,  31 
penetration  of,  30 
production  of,  24 
protection  from,  190 
tube,  61 

connected  to  the  coil  of  trans- 
former, 63 

essential  parts,  61 

types  of,  61,  65,  66,  67,  68 

vacuum  of,  61 


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